Organic element for electroluminescent devices

ABSTRACT

An electroluminescent device comprising a host material and a rubrene derivative having a naphthacene nucleus comprising four fused phenyl rings a, b, c, and d, in order, containing two secondary phenyl ring groups linked to the “c” ring, each bearing directly or indirectly a fluoro or perfluoroalkyl group, wherein each fluoro or perfluoroalkyl group is either:
         a) linked directly to one of said secondary phenyl rings and is located on a meta or ortho position, or   b) located in any position of another aryl group linked directly or indirectly to one of the secondary phenyl rings.

FIELD OF THE INVENTION

This invention relates to an electroluminescent (EL) device comprising alight-emitting layer containing a rubrene derivative containing fluorineor fluorine-containing groups.

BACKGROUND OF THE INVENTION

While organic electroluminescent (EL) devices have been known for overtwo decades, their performance limitations have represented a barrier tomany desirable applications. In simplest form, an organic EL device iscomprised of an anode for hole injection, a cathode for electroninjection, and an organic medium sandwiched between these electrodes tosupport charge recombination that yields emission of light. Thesedevices are also commonly referred to as organic light-emitting diodes,or OLEDs. Representative of earlier organic EL devices are Gurnee et al.U.S. Pat. No. 3,172,862, issued Mar. 9, 1965; Gurnee U.S. Pat. No.3,173,050, issued Mar. 9, 1965; Dresner, “Double InjectionElectroluminescence in Anthracene”, RCA Review, 30, 322–334, (1969); andDresner U.S. Pat. No. 3,710,167, issued Jan. 9, 1973. The organic layersin these devices, usually composed of a polycyclic aromatic hydrocarbon,were very thick (much greater than 1 μm). Consequently, operatingvoltages were very high, often greater than 100V.

More recent organic EL devices include an organic EL element consistingof extremely thin layers (e.g., less than 1.0 μm) between the anode andthe cathode. Herein, the term “organic EL element” encompasses thelayers between the anode and cathode. Reducing the thickness lowered theresistance of the organic layer and has enabled devices that operate atmuch lower voltage. In a basic two-layer EL device structure, describedfirst in U.S. Pat. No. 4,356,429, one organic layer of the EL elementadjacent to the anode is specifically chosen to transport holes, andtherefore, it is referred to as the hole-transporting layer, and theother organic layer is specifically chosen to transport electrons, andis referred to as the electron-transporting layer. Recombination of theinjected holes and electrons within the organic EL element results inefficient electroluminescence.

There have also been proposed three-layer organic EL devices thatcontain an organic light-emitting layer (LEL) between thehole-transporting layer and electron-transporting layer, such as thatdisclosed by Tang et al (J. Applied Physics, 65, Pages 3610–3616,(1989)). The light-emitting layer commonly consists of a host materialdoped with a guest material, also known as a dopant. Still further,there has been proposed in U.S. Pat. No. 4,769,292 a four-layer ELelement comprising a hole-injecting layer (HIL), a hole-transportinglayer (HTL), a light-emitting layer (LEL) and an electrontransport/injection layer (ETL). These structures have resulted inimproved device efficiency.

Since these early inventions, further improvements in device materialshave resulted in improved performance in attributes such as color,stability, luminance efficiency and manufacturability, e.g., asdisclosed in U.S. Pat. No. 5,061,569, U.S. Pat. No. 5,409,783, U.S. Pat.No. 5,554,450, U.S. Pat. No. 5,593,788, U.S. Pat. No. 5,683,823, U.S.Pat. No. 5,908,581, U.S. Pat. No. 5,928,802, U.S. Pat. No. 6,020,078,and U.S. Pat. No. 6,208,077, amongst others.

Notwithstanding these developments, there are continuing needs fororganic EL device components, such as light-emitting materials,sometimes referred to as dopants, that will provide high luminanceefficiencies combined with high color purity and long lifetimes. Inparticular, there is a need to be able to adjust the emission wavelengthof the light-emitting material for various applications. For example, inaddition to the need for blue, green, and red light-emitting materialsthere is a need for blue-green, yellow and orange light-emittingmaterials in order to formulate white-light emitting electroluminescentdevices. For example, a device can emit white light by emitting acombination of colors, such as blue-green light and red light or acombination of blue light and orange light.

White EL devices can be used with color filters in full-color displaydevices. They can also be used with color filters in other multicolor orfunctional-color display devices. White EL devices for use in suchdisplay devices are easy to manufacture, and they produce reliable whitelight in each pixel of the displays. Although the OLEDs are referred toas white they can appear white or off-white, the CIE coordinates of thelight emitted by the OLED are less important than the requirement thatthe spectral components passed by each of the color filters be presentwith sufficient intensity in that light. The devices must also have goodstability in long-term operation. That is, as the devices are operatedfor extended periods of time, the luminance of the devices shoulddecrease as little as possible.

A useful class of dopants is that derived from5,6,11,12-tetraphenylnaphthacene, also referred to as rubrene. Thesolution spectra of these materials are typically characterized bywavelength of maximum emission, also referred to as emission λ_(max), ina range of 550–560 nm and are useful in organic EL devices incombination with dopants in other layers to produce white light. Use ofthese rubrene-derived dopants in EL devices depends on whether thematerial sublimes. If the material melts, its use as a dopant islimited. Sublimation and deposition are the processes by which thedopant, subjected to high temperature and low pressure passes from thesolid phase to the gas phase and back to the solid phase and in theprocess is deposited onto the device. Depending on the chemicalstructure of the dopant, when the temperature needed to sublime thedopant is high, thermal decomposition can occur. If the decompositionproducts also sublime the device can become contaminated. Decompositionleads to the inefficient use of dopant. Contamination with decompositionproducts can cause the device to have shorter operational lifetimes andcan contribute to color degradation and light purity. In order toachieve OLEDs that can produce high purity white light, have goodstability and no contamination from dopant decomposition, in addition toefficient use of dopant, one needs to have the ability to lower thesublimation temperature.

Useful dopants are those that emit light in ethyl acetate solution inthe range of 530–650 nm, have good efficiency and sublime readily.

U.S. Pat. No. 6,387,547B1; U.S. Pat. No. 6,399,223B1; and EP 1,148,109A2teaches the use of rubrene derivatives containing either 2 phenyl groupson one end ring of the rubrene structure or 4 phenyl groups on both endrings. There is no teaching of fluorine or fluorine-containing groups onthe rubrene structure.

JP 04335087A discloses specific compounds 6, 13 and 14 containingchlorine or bromine at various positions on the rubrene molecule.

WO 02100977A1 discloses compound “C12” with two heterocyclic aromaticfluorine-containing groups also on the 5- and 12-positions of thenaphthacene nucleus.

JP 10289786A discloses compound “15” with fluoro- groups on thepara-positions of the secondary phenyl rings at the 5- and 12-positionsof the naphthacene nucleus. U.S. Ser. No. 10/700,894filed Nov. 4, 2003,describes fluorine containing rubrenes for lowering the sublimationtemperature where there are certain fluoro group arrangements.

However, high sublimation temperatures and possible decomposition wouldlimit the use of many of these rubrene derivatives. Some of thesematerials would also be limited in the range of hues that they couldprovide. Devices containing many rubrene derivatives would fail toprovide consistent white OLED devices with high color purity and reducedpotential for possible contamination from decomposition impurities intheir deposition. It is a problem to be solved to provide an OLED deviceusing materials that can be sublimed at a lower temperature thusproviding a lowered level of decomposition during the vacuum depositionprocess.

SUMMARY OF THE INVENTION

The invention provides an electroluminescent device comprising a hostmaterial and a rubrene derivative having a naphthacene nucleuscomprising four fused phenyl rings a, b, c, and d, in order, containingtwo secondary phenyl ring groups linked to the “c” ring, each bearingdirectly or indirectly a fluoro or perfluoroalkyl group, wherein eachfluoro or perfluoroalkyl group is either:

a) linked directly to one of said secondary phenyl rings and is locatedon a meta or ortho position, or

b) located in any position of another aryl group linked directly orindirectly to one of the secondary phenyl rings.

The invention also provides displays and area lighting devicescontaining the device and a process for emitting light employing thedevice. The device is advantageous because the materials can be sublimedat a lower temperature thus providing a lowered level of decompositionduring a vacuum deposition process.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows a cross-section of a typical OLED device in which thisinvention may be used.

DETAILED DESCRIPTION OF THE INVENTION

An electroluminescent device of the invention may be a multilayer devicecomprising a cathode, an anode, charge-injecting layers (if necessary),charge-transporting layers, and a light-emitting layer (LEL) comprisinga host and at least one light-emitting material. Desirably thelight-emitting layer comprises a host material and a rubrene derivative.

The term rubrene refers to a 5,6,11,12-tetraphenylnaphthacene as definedby the Grant & Hackh's Chemical Dictionary, Fifth Edition, McGraw-HillBook Company, page 512 and Dictionary of Organic Compounds, FifthEdition, Chapman and Hall, Volume 5, page 5297. The term naphthacene isthe chemical name used to describe four linearly fused benzene rings asdefined by the Grant & Hackh's Chemical Dictionary, Fifth Edition,McGraw-Hill Book Company, page 383. The four rings of the rubenenaphthacene nucleus can be labeled as the a, b, c, and d rings as shownbelow.

In one desirable embodiment the rubrene derivative of the inventioncontains at least one phenyl ring on the “c” ring bearing a fluoro groupor a fluorine containing alkyl group on a meta or ortho position of thatphenyl ring. In one embodiment, the fluorine containing alkyl group is aperfluoroalkyl group, which is an alkyl group that is fully substitutedwith fluoro substituents, for example a trifluoromethyl orpentafluoroethyl group.

In another desirable embodiment the rubrene derivative of the inventioncontains at least one secondary phenyl ring on the “c” ring, which islinked to, that is substituted with, a further aryl group.Alternatively, the phenyl ring may be indirectly linked to the arylring. That is the secondary phenyl ring may be bonded to another group,which in turn may be bonded to the aryl ring. The aryl group contains afluoro or perfluoroalkyl substituent. In this case the fluoro orperfluoroalkyl group is not restricted to be in a meta or ortho positionof the aryl group. The term aryl group is intended to include onlyaromatic groups of one or more than one fused rings having only carbonring members and not heteroatomic group ring members.

In one desirable embodiment, the aryl group is a phenyl group that issubstituted with a fluoro or perfluoroalkyl group, suitably the phenylgroup is substituted with a meta- or para-fluoro substituent.

Desirably, the rubrene derivative is represented by Formula (1).

In Formula (1) Ar₁, Ar₂, and Ar₃ represent independently selected arylgroups, for example phenyl groups or tolyl groups. Each G represents anindependently selected substituent, such as an alkyl group, for examplea methyl group. Each m is independently 0–4. In Formula (1), V¹–V⁵represent hydrogen or independently selected substituent groups, such asan alkyl or an aryl groups, provided there are in total two fluoro orperfluoroalkyl groups linked directly or indirectly to the “c” ring,selected from those where at least one of V¹–V⁴ represents a fluoro orperfluoroalkyl group, or at least one of V¹–V⁵ and AR₃ includes an arylgroup bearing a fluoro or trifluoromethyl group.

In one suitable embodiment, V³ of Formula 1 represents a fluorosubstituent. In another suitable embodiment, at least one of V², V³, andV⁵ includes a phenyl ring bearing a fluoro or perfluoroalkyl group.

Substituents on the rubrene derivative of the invention are selected toprovide embodiments that exhibit a reduced loss of initial luminancecompared to the device containing no naphthacene compound.

Embodiments of the dopants useful in the invention provide an EL deviceemitting light with yellow, yellow-orange, orange, orange-red or redhues. Suitably the substituents of the rubrene derivative are selectedto provide an emitted light having a wavelength of maximum emission(λ_(max)) in ethyl acetate solution such that λ_(max) is greater orequal to 520 nm and less than or equal to 650 nm, have good efficiencyand sublime at low temperatures. Combined with other light-emittingdopants, the dopants of the invention can be used to produce whitelight.

In one embodiment, the substituents of the rubrene derivative areselected to provide an emitted light having an orange-red hue. Therubrene derivative may be used in a device that also comprises anotherlight-emitting dopant that emits blue or blue-green light.

Blue light is generally defined as having a wavelength range in thevisible region of the electromagnetic spectrum of 450–480 nm, blue-green480–510 nm, green 510–550, green-yellow 550–570 nm, yellow 570–590 nm,orange 590–630 nm and red 630–700 nm, as defined by Dr. R. W. G. Hunt inThe Reproduction of Colour in Photography, Printing & Television, 4^(th)Edition 1987, Fountain Press, page 4. Suitable combinations of thesecomponents produce white light. When light has a spectral profile thatoverlaps these ranges, to whatever degree, it is loosely referred to ashaving both color components for example, yellow-orange or orange-red.

Many materials that emit blue or blue-green light are known in the artand are contemplated for use in the practice of the present invention.Particularly useful classes of blue emitters include perylene and itsderivatives such as a perylene nucleus bearing one or more substituentssuch as an alkyl group or an aryl group. A desirable perylene derivativefor use as a blue emitting material is 2,5,8,11-tetra-t-butylperylene.

Another useful class of fluorescent materials includes blue orblue-green light emitting derivatives of distyrylarenes, such asdistyrylbenzene and distyrylbiphenyl, including compounds described inU.S. Pat. No. 5,121,029. Among derivatives of distyrylarenes thatprovide blue or blue-green luminescence, particularly useful are thosesubstituted with diarylamino groups, also known as distyrylamines.Examples include Formula 2a and 2b, listed below, wherein R^(a)–R^(j)can be the same or different, and individually represent hydrogen or oneor more substituents. For example, substituents can be alkyl groups,such as methyl groups, or aryl groups, such as phenyl groups.

Illustrative examples of useful distyrylamines are blue or blue greenemitters, (2c) and (2d) listed below.

Another useful class of blue or blue green emitters comprise a boronatom. Desirable light-emitting materials that contain boron includethose described in US 20030198829A1 and US 20030201415A1. Suitable blueor blue-green light-emitting materials are represented by the structureFormula (3a).

In Formula (3a), Ar^(a) and Ar^(b) independently represent the atomsnecessary to form a five or six-membered aromatic ring group, such as apyridine group. Z^(a) and Z^(b) represent independently selectedsubstituents, such as fluoro substituents. In Formula (3a), w representsN or C—Y, wherein Y represents hydrogen or a substituent, such as anaromatic group, such as a phenyl group or a tolyl group, an alkyl group,such as a methyl group, a cyano substituent, or a trifluoromethylsubstituent.

Illustrative examples of useful boron-containing blue fluorescentmaterials are listed below.

In one embodiment of the invention, the device further comprises ared-light-emitting compound to provide a white light emission. In onedesirable embodiment the red-light-emitting compound is adiindenoperylene compound of Formula (4a).

In Formula (4a), R₁–R₁₆ are independently selected as hydrogen orsubstituent groups that provide red luminescence; see, for example, U.S.patent application Ser. No. 10/334,324, and provided that any of theindicated substituents can join to form further fused rings.

Particularly useful diindenoperylene dopants that provide redluminescence are those in which R₁–R₁₆ are independently selected fromthe category including hydrogen and aryl groups, including aryl ringgroups fused to the diindenoperylene skeleton, as illustrated by theformulas shown below. In one desirable embodiment R₁, R₄, R₉, R₁₂ ofFormula (4a) represent independently selected phenyl groups, R₂, and R₃as well as R₁₀ and R₁₁ form independently selected fused benzene ringgroups.

When a material of Formula (4a) is present, the rubrene derivative ofthe invention may not emit light, but instead transfer energy to thediindenoperylene derivative of Formula (4a), which in turn emits redlight.

The electroluminescent device comprises, in addition to a rubrenederivative, a host material. Suitably, the rubrene derivative is presentin an amount of up to 25%-wt of the host, typically up to 15% and moretypically up to 10% and commonly from 0.1–5.0%-wt of the host.

The host may be a hole-transporting material. For example the host maybe a tertiary amine or a mixture of such compounds. Examples of usefulhole-transporting materials are4,4′-bis[N-(1-naphthyl)-N-phenylamino]biphenyl (NPB), and4,4′-bis[N-(1-naphthyl)-N-(2-naphthyl)amino]biphenyl (TNB).

The host may be an electron-transporting material. Metal complexes of8-hydroxyquinoline and similar derivatives, also known as metal-chelatedoxinoid compounds, constitute a class of useful host compounds. Anespecially useful example of electron-transporting host material istris(8-quinolinolato)aluminum(III) (AlQ).

In another embodiment of the invention, when additional layers arepresent so that the emitted light is white, a filter capable ofcontrolling the spectral components of the white light such as red,green and blue, can be placed over-lying the device to give a deviceuseful for color display.

The rubrene derivative may also be an oligomer or a polymer having amain chain or a side chain of repeating units. The rubrene derivativemay be provided as a discrete material dispersed in the host material,or it may be bonded in some way to the host material, for example,covalently bonded into a polymeric host. In one useful embodiment, atleast one layer of the EL device, comprises polymeric material. Inanother suitable embodiment, at least two layers of the EL devicecomprise polymeric material.

Rubrene derivatives useful in the present invention may be synthesizedby various methods known in the literature. For example see J. Dodge, J.Bain, R. Chamberlin, J. of Org. Chem., 55, 4190 (1990) and A. Essenfeld,U.S. Pat. No. 4,855,520 and references cited therein.

Illustrative examples of rubrene derivatives useful in the presentinvention include the following compounds.

Unless otherwise specifically stated, use of the term “substituted” or“substituent” means any group or atom other than hydrogen. Additionally,when the term “group” is used, it means that when a substituent groupcontains a substitutable hydrogen, it is also intended to encompass notonly the substituent's unsubstituted form, but also its form furthersubstituted with any substituent group or groups as herein mentioned, solong as the substituent does not destroy properties necessary for deviceutility. Suitably, a substituent group may be halogen or may be bondedto the remainder of the molecule by an atom of carbon, silicon, oxygen,nitrogen, phosphorous, sulfur, selenium, or boron. The substituent maybe, for example, halogen, such as chloro, bromo or fluoro; nitro;hydroxyl; cyano; carboxyl; or groups which may be further substituted,such as alkyl, including straight or branched chain or cyclic alkyl,such as methyl, trifluoromethyl, ethyl, t-butyl,3-(2,4-di-t-pentylphenoxy) propyl, and tetradecyl; alkenyl, such asethylene, 2-butene; alkoxy, such as methoxy, ethoxy, propoxy, butoxy,2-methoxyethoxy, sec-butoxy, hexyloxy, 2-ethylhexyloxy, tetradecyloxy,2-(2,4-di-t-pentylphenoxy)ethoxy, and 2-dodecyloxyethoxy; aryl such asphenyl, 4-t-butylphenyl, 2,4,6-trimethylphenyl, naphthyl; aryloxy, suchas phenoxy, 2-methylphenoxy, alpha- or beta-naphthyloxy, and 4-tolyloxy;carbonamido, such as acetamido, benzamido, butyramido, tetradecanamido,alpha-(2,4-di-t-pentylphenoxy)acetamido,alpha-(2,4-di-t-pentylphenoxy)butyramido,alpha-(3-pentadecylphenoxy)-hexanamido,alpha-(4-hydroxy-3-t-butylphenoxy)-tetradecanamido,2-oxo-pyrrolidin-1-yl, 2-oxo-5-tetradecylpyrrolin-1-yl,N-methyltetradecanamido, N-succinimido, N-phthalimido,2,5-dioxo-1-oxazolidinyl, 3-dodecyl-2,5-dioxo-1-imidazolyl, andN-acetyl-N-dodecylamino, ethoxycarbonylamino, phenoxycarbonylamino,benzyloxycarbonylamino, hexadecyloxycarbonylamino,2,4-di-t-butylphenoxycarbonylamino, phenylcarbonylamino,2,5-(di-t-pentylphenyl)carbonylamino, p-dodecylphenylcarbonylamino,p-tolylcarbonylamino, N-methylureido, N,N-dimethylureido,N-methyl-N-dodecylureido, N-hexadecylureido, N,N-dioctadecylureido,N,N-dioctyl-N′-ethylureido, N-phenylureido, N,N-diphenylureido,N-phenyl-N-p-tolylureido, N-(m-hexadecylphenyl)ureido,N,N-(2,5-di-t-pentylphenyl)-N′-ethylureido, and t-butylcarbonamido;sulfonamido, such as methylsulfonamido, benzenesulfonamido,p-tolylsulfonamido, p-dodecylbenzenesulfonamido,N-methyltetradecylsulfonamido, N,N-dipropylsulfamoylamino, andhexadecylsulfonamido; sulfamoyl, such as N-methylsulfamoyl,N-ethylsulfamoyl, N,N-dipropylsulfamoyl, N-hexadecylsulfamoyl,N,N-dimethylsulfamoyl, N-[3-(dodecyloxy)propyl]sulfamoyl,N-[4-(2,4-di-t-pentylphenoxy)butyl]sulfamoyl,N-methyl-N-tetradecylsulfamoyl, and N-dodecylsulfamoyl; carbamoyl, suchas N-methylcarbamoyl, N,N-dibutylcarbamoyl, N-octadecylcarbamoyl,N-[4-(2,4-di-t-pentylphenoxy)butyl]carbamoyl,N-methyl-N-tetradecylcarbamoyl, and N,N-dioctylcarbamoyl; acyl, such asacetyl, (2,4-di-t-amylphenoxy)acetyl, phenoxycarbonyl,p-dodecyloxyphenoxycarbonyl methoxycarbonyl, butoxycarbonyl,tetradecyloxycarbonyl, ethoxycarbonyl, benzyloxycarbonyl,3-pentadecyloxycarbonyl, and dodecyloxycarbonyl; sulfonyl, such asmethoxysulfonyl, octyloxysulfonyl, tetradecyloxysulfonyl,2-ethylhexyloxysulfonyl, phenoxysulfonyl,2,4-di-t-pentylphenoxysulfonyl, methylsulfonyl, octylsulfonyl,2-ethylhexylsulfonyl, dodecylsulfonyl, hexadecylsulfonyl,phenylsulfonyl, 4-nonylphenylsulfonyl, and p-tolylsulfonyl; sulfonyloxy,such as dodecylsulfonyloxy, and hexadecylsulfonyloxy; sulfinyl, such asmethylsulfinyl, octylsulfinyl, 2-ethylhexylsulfinyl, dodecylsulfinyl,hexadecylsulfinyl, phenylsulfinyl, 4-nonylphenylsulfinyl, andp-tolylsulfinyl; thio, such as ethylthio, octylthio, benzylthio,tetradecylthio, 2-(2,4-di-t-pentylphenoxy)ethylthio, phenylthio,2-butoxy-5-t-octylphenylthio, and p-tolylthio; acyloxy, such asacetyloxy, benzoyloxy, octadecanoyloxy, p-dodecylamidobenzoyloxy,N-phenylcarbamoyloxy, N-ethylcarbamoyloxy, and cyclohexylcarbonyloxy;amine, such as phenylanilino, 2-chloroanilino, diethylamine,dodecylamine; imino, such as 1 (N-phenylimido)ethyl, N-succinimido or3-benzylhydantoinyl; phosphate, such as dimethylphosphate andethylbutylphosphate; phosphite, such as diethyl and dihexylphosphite; aheterocyclic group, a heterocyclic oxy group or a heterocyclic thiogroup, each of which may be substituted and which contain a 3 to 7membered heterocyclic ring composed of carbon atoms and at least onehetero atom selected from the group consisting of oxygen, nitrogen,sulfur, phosphorous, or boron. such as 2-furyl, 2-thienyl,2-benzimidazolyloxy or 2-benzothiazolyl; quaternary ammonium, such astriethylammonium; quaternary phosphonium, such as triphenylphosphonium;and silyloxy, such as trimethylsilyloxy.

If desired, the substituents may themselves be further substituted oneor more times with the described substituent groups. The particularsubstituents used may be selected by those skilled in the art to attainthe desired desirable properties for a specific application and caninclude, for example, electron-withdrawing groups, electron-donatinggroups, and steric groups. When a molecule may have two or moresubstituents, the substituents may be joined together to form a ringsuch as a fused ring unless otherwise provided. Generally, the abovegroups and substituents thereof may include those having up to 48 carbonatoms, typically 1 to 36 carbon atoms and usually less than 24 carbonatoms, but greater numbers are possible depending on the particularsubstituents selected.

General Device Architecture

The present invention can be employed in many EL device configurationsusing small molecule materials, oligomeric materials, polymericmaterials, or combinations thereof. These include very simple structurescomprising a single anode and cathode to more complex devices, such aspassive matrix displays comprised of orthogonal arrays of anodes andcathodes to form pixels, and active-matrix displays where each pixel iscontrolled independently, for example, with thin film transistors(TFTs).

There are numerous configurations of the organic layers wherein thepresent invention can be successfully practiced. The essentialrequirements of an OLED are an anode, a cathode, and an organiclight-emitting layer located between the anode and cathode. Additionallayers may be employed as more fully described hereafter.

A typical structure according to the present invention and especiallyuseful for a small molecule device, is shown in FIG. 1 and is comprisedof a substrate 101, an anode 103, a hole-injecting layer 105, ahole-transporting layer 107, a light-emitting layer 109, anelectron-transporting layer 111, and a cathode 113. These layers aredescribed in detail below. Note that the substrate 101 may alternativelybe located adjacent to the cathode 113, or the substrate 101 mayactually constitute the anode 103 or cathode 113. The organic layersbetween the anode 103 and cathode 113 are conveniently referred to asthe organic EL element. Also, the total combined thickness of theorganic layers is desirably less than 500 nm. If the device includesphosphorescent material, a hole-blocking layer, located between thelight-emitting layer and the electron-transporting layer, may bepresent.

The anode 103 and cathode 113 of the OLED are connected to avoltage/current source through electrical conductors. The OLED isoperated by applying a potential between the anode 103 and cathode 113such that the anode 103 is at a more positive potential than the cathode113. Holes are injected into the organic EL element from the anode 103and electrons are injected into the organic EL element at the cathode113. Enhanced device stability can sometimes be achieved when the OLEDis operated in an AC mode where, for some time period in the AC cycle,the potential bias is reversed and no current flows. An example of an ACdriven OLED is described in U.S. Pat. No. 5,552,678.

Substrate

The OLED device of this invention is typically provided over asupporting substrate 101 where either the cathode 113 or anode 103 canbe in contact with the substrate. The electrode in contact with thesubstrate 101 is conveniently referred to as the bottom electrode.Conventionally, the bottom electrode is the anode 103, but thisinvention is not limited to that configuration. The substrate 101 caneither be light transmissive or opaque, depending on the intendeddirection of light emission. The light transmissive property isdesirable for viewing the EL emission through the substrate 101.Transparent glass or plastic is commonly employed in such cases. Thesubstrate 101 can be a complex structure comprising multiple layers ofmaterials. This is typically the case for active matrix substrateswherein TFTs are provided below the OLED layers. It is still necessarythat the substrate 101, at least in the emissive pixelated areas, becomprised of largely transparent materials such as glass or polymers.For applications where the EL emission is viewed through the topelectrode, the transmissive characteristic of the bottom support isimmaterial, and therefore the substrate can be light transmissive, lightabsorbing or light reflective. Substrates for use in this case include,but are not limited to, glass, plastic, semiconductor materials such assilicon, ceramics, and circuit board materials. Again, the substrate 101can be a complex structure comprising multiple layers of materials suchas found in active matrix TFT designs. It is necessary to provide inthese device configurations a light-transparent top electrode.

Anode

When the desired electroluminescent light emission (EL) is viewedthrough the anode, the anode 103 should be transparent or substantiallytransparent to the emission of interest. Common transparent anodematerials used in this invention are indium-tin oxide (ITO), indium-zincoxide (IZO) and tin oxide, but other metal oxides can work including,but not limited to, aluminum- or indium-doped zinc oxide,magnesium-indium oxide, and nickel-tungsten oxide. In addition to theseoxides, metal nitrides, such as gallium nitride, and metal selenides,such as zinc selenide, and metal sulfides, such as zinc sulfide, can beused as the anode 103. For applications where EL emission is viewed onlythrough the cathode 113, the transmissive characteristics of the anode103 are immaterial and any conductive material can be used, transparent,opaque or reflective. Example conductors for this application include,but are not limited to, gold, iridium, molybdenum, palladium, andplatinum. Typical anode materials, transmissive or otherwise, have awork function of 4.1 eV or greater. Desired anode materials are commonlydeposited by any suitable means such as evaporation, sputtering,chemical vapor deposition, or electrochemical means. Anodes can bepatterned using well-known photolithographic processes. Optionally,anodes may be polished prior to application of other layers to reducesurface roughness so as to minimize short circuits or enhancereflectivity.

Cathode

When light emission is viewed solely through the anode 103, the cathode113 used in this invention can be comprised of nearly any conductivematerial. Desirable materials have good film-forming properties toensure good contact with the underlying organic layer, promote electroninjection at low voltage, and have good stability. Useful cathodematerials often contain a low work function metal (<4.0 eV) or metalalloy. One useful cathode material is comprised of a Mg:Ag alloy whereinthe percentage of silver is in the range of 1 to 20%, as described inU.S. Pat. No. 4,885,221. Another suitable class of cathode materialsincludes bilayers comprising the cathode and a thin electron-injectionlayer (EIL) in contact with an organic layer (e.g., an electrontransporting layer (ETL)), the cathode being capped with a thicker layerof a conductive metal. Here, the EIL preferably includes a low workfunction metal or metal salt, and if so, the thicker capping layer doesnot need to have a low work function. One such cathode is comprised of athin layer of LiF followed by a thicker layer of Al as described in U.S.Pat. No. 5,677,572. An ETL material doped with an alkali metal, forexample, Li-doped Alq, is another example of a useful EIL. Other usefulcathode material sets include, but are not limited to, those disclosedin U.S. Pat. Nos. 5,059,861, 5,059,862, and 6,140,763.

When light emission is viewed through the cathode, the cathode 113 mustbe transparent or nearly transparent. For such applications, metals mustbe thin or one must use transparent conductive oxides, or a combinationof these materials. Optically transparent cathodes have been describedin more detail in U.S. Pat. No. 4,885,211, U.S. Pat. No. 5,247,190, JP3,234,963, U.S. Pat. No. 5,703,436, U.S. Pat. No. 5,608,287, U.S. Pat.No. 5,837,391, U.S. Pat. No. 5,677,572, U.S. Pat. No. 5,776,622, U.S.Pat. No. 5,776,623, U.S. Pat. No. 5,714,838, U.S. Pat. No. 5,969,474,U.S. Pat. No. 5,739,545, U.S. Pat. No. 5,981,306, U.S. Pat. No.6,137,223, U.S. Pat. No. 6,140,763, U.S. Pat. No. 6,172,459, EP 1 076368, U.S. Pat. No. 6,278,236, and U.S. Pat. No. 6,284,3936. Cathodematerials are typically deposited by any suitable method such asevaporation, sputtering, or chemical vapor deposition. When needed,patterning can be achieved through many well known methods including,but not limited to, through-mask deposition, integral shadow masking asdescribed in U.S. Pat. No. 5,276,380 and EP 0 732 868, laser ablation,and selective chemical vapor deposition.

Hole-Injecting Layer (HIL)

A hole-injecting layer 105 may be provided between anode 103 andhole-transporting layer 107. The hole-injecting layer can serve toimprove the film formation property of subsequent organic layers and tofacilitate injection of holes into the hole-transporting layer 107.Suitable materials for use in the hole-injecting layer 105 include, butare not limited to, porphyrinic compounds as described in U.S. Pat. No.4,720,432, plasma-deposited fluorocarbon polymers as described in U.S.Pat. No. 6,208,075, and some aromatic amines, for example, MTDATA(4,4′,4″-tris[(3-methylphenyl)phenylamino]triphenylamine). Alternativehole-injecting materials reportedly useful in organic EL devices aredescribed in EP 0 891 121 A1 and EP 1 029 909 A1. A hole-injection layeris conveniently used in the present invention, and is desirably aplasma-deposited fluorocarbon polymer. The thickness of a hole-injectionlayer containing a plasma-deposited fluorocarbon polymer can be in therange of 0.2 nm to 15 nm and suitably in the range of 0.3 to 1.5 nm.

Hole-Transporting Layer (HTL)

While not always necessary, it is often useful to include ahole-transporting layer in an OLED device. The hole-transporting layer107 of the organic EL device contains at least one hole-transportingcompound such as an aromatic tertiary amine, where the latter isunderstood to be a compound containing at least one trivalent nitrogenatom that is bonded only to carbon atoms, at least one of which is amember of an aromatic ring. In one form the aromatic tertiary amine canbe an arylamine, such as a monoarylamine, diarylamine, triarylamine, ora polymeric arylamine. Exemplary monomeric triarylamines are illustratedby Klupfel et al. U.S. Pat. No. 3,180,730. Other suitable triarylaminessubstituted with one or more vinyl radicals and/or comprising at leastone active hydrogen containing group are disclosed by Brantley et alU.S. Pat. No. 3,567,450 and U.S. Pat. No. 3,658,520.

A more preferred class of aromatic tertiary amines is those whichinclude at least two aromatic tertiary amine moieties as described inU.S. Pat. No. 4,720,432 and U.S. Pat. No. 5,061,569. Such compoundsinclude those represented by structural formula (A).

wherein Q₁ and Q₂ are independently selected aromatic tertiary aminemoieties and G is a linking group such as an arylene, cycloalkylene, oralkylene group of a carbon to carbon bond. In one embodiment, at leastone of Q₁ or Q₂ contains a polycyclic fused ring structure, e.g., anaphthalene. When G is an aryl group, it is conveniently a phenylene,biphenylene, or naphthalene moiety.

A useful class of triarylamines satisfying structural formula (A) andcontaining two triarylamine moieties is represented by structuralformula (B):

where

-   -   R₁ and R₂ each independently represents a hydrogen atom, an aryl        group, or an alkyl group or R₁ and R₂ together represent the        atoms completing a cycloalkyl group; and    -   R₃ and R₄ each independently represents an aryl group, which is        in turn substituted with a diaryl substituted amino group, as        indicated by structural formula (C):

wherein R₅ and R₆ are independently selected aryl groups. In oneembodiment, at least one of R₅ or R₆ contains a polycyclic fused ringstructure, e.g., a naphthalene.

Another class of aromatic tertiary amines is the tetraaryldiamines.Desirable tetraaryldiamines include two diarylamino groups, such asindicated by formula (C), linked through an arylene group. Usefultetraaryldiamines include those represented by formula (D).

wherein

-   -   each Are is an independently selected arylene group, such as a        phenylene or anthracene moiety,    -   n is an integer of from 1 to 4, and    -   Ar, R₇, R₈, and R₉ are independently selected aryl groups.

In a typical embodiment, at least one of Ar, R₇, R₈, and R₉ is apolycyclic fused ring structure, e.g., a naphthalene.

The various alkyl, alkylene, aryl, and arylene moieties of the foregoingstructural formulae (A), (B), (C), (D), can each in turn be substituted.Typical substituents include alkyl groups, alkoxy groups, aryl groups,aryloxy groups, and halide such as fluoride, chloride, and bromide. Thevarious alkyl and alkylene moieties typically contain from about 1 to 6carbon atoms. The cycloalkyl moieties can contain from 3 to about 10carbon atoms, but typically contain five, six, or seven ring carbonatoms—e.g., cyclopentyl, cyclohexyl, and cycloheptyl ring structures.The aryl and arylene moieties are usually phenyl and phenylene moieties.

The hole-transporting layer can be formed of a single tertiary aminecompound or a mixture of such compounds. Specifically, one may employ atriarylamine, such as a triarylanine satisfying the formula (B), incombination with a tetraaryldiamine, such as indicated by formula (D).Illustrative of useful aromatic tertiary amines are the following:

-   -   1,1-Bis(4-di-p-tolylaminophenyl)cyclohexane (TAPC)    -   1,1-Bis(4-di-p-tolylaminophenyl)-4-methylcyclohexane    -   1,1-Bis(4-di-p-tolylaminophenyl)-4-phenylcyclohexane    -   1,1-Bis(4-di-p-tolylaminophenyl)-3-phenylpropane (TAPPP)    -   N,N,N′,N′-tetraphenyl-4,4′″-diamino-1,1′:4′,1″:4″,1′″-quaterphenyl    -   Bis(4-dimethylamino-2-methylphenyl)phenylmethane    -   1,4-bis[2-[4-[N,N-di(p-toly)amino]phenyl]vinyl]benzene (BDTAPVB)    -   N,N,N′,N′-Tetra-p-tolyl-4,4′-diaminobiphenyl (TTB)    -   N,N,N′,N′-Tetraphenyl-4,4′-diaminobiphenyl    -   N,N,N′,N′-tetra-1-naphthyl-4,4′-diaminobiphenyl    -   N,N,N′,N′-tetra-2-naphthyl-4,4′-diaminobiphenyl    -   N-Phenylcarbazole    -   4,4′-Bis[N-(1-naphthyl)-N-phenylamino]biphenyl (NPB)    -   4,4′-Bis[N-(1-naphthyl)-N-(2-naphthyl)amino]biphenyl (TNB)    -   4,4′-Bis[N-(1-naphthyl)-N-phenylamino]p-terphenyl    -   4,4′-Bis[N-(2-naphthyl)-N-phenylamino]biphenyl    -   4,4′-Bis[N-(3-acenaphthenyl)-N-phenylamino]biphenyl    -   1,5-Bis[N-(1-naphthyl)-N-phenylamino]naphthalene    -   4,4′-Bis[N-(9-anthryl)-N-phenylamino]biphenyl    -   4,4′-Bis[N-(1-anthryl)-N-phenylamino]-p-terphenyl    -   4,4′-Bis[N-(2-phenanthryl)-N-phenylamino]biphenyl    -   4,4′-Bis[N-(8-fluoranthenyl)-N-phenylamino]biphenyl    -   4,4′-Bis[N-(2-pyrenyl)-N-phenylamino]biphenyl    -   4,4′-Bis[N-(2-naphthacenyl)-N-phenylamino]biphenyl    -   4,4′-Bis[N-(2-perylenyl)-N-phenylamino]biphenyl    -   4,4′-Bis[N-(1-coronenyl)-N-phenylamino]biphenyl    -   2,6-Bis(di-p-tolylamino)naphthalene    -   2,6-Bis[di-(1-naphthyl)amino]naphthalene    -   2,6-Bis[N-(1-naphthyl)-N-(2-naphthyl)amino]naphthalene    -   N,N,N′,N′-Tetra(2-naphthyl)-4,4″-diamino-p-terphenyl    -   4,4′-Bis{N-phenyl-N-[4-(1-naphthyl)-phenyl]amino}biphenyl    -   2,6-Bis[N,N-di(2-naphthyl)amino]fluorene    -   4,4′,4″-tris[(3-methylphenyl)phenylamino]triphenylamine (MTDATA)

-   4,4′-Bis[N-(3-methylphenyl)-N-phenylamino]biphenyl (TPD)

Another class of useful hole-transporting materials includes polycyclicaromatic compounds as described in EP 1 009 041. Tertiary aromaticamines with more than two amine groups may be used including oligomericmaterials. In addition, polymeric hole-transporting materials can beused such as poly(N-vinylcarbazole) (PVK), polythiophenes, polypyrrole,polyaniline, and copolymers such aspoly(3,4-ethylenedioxythiophene)/poly(4-styrenesulfonate) also calledPEDOT/PSS. It is also possible for the hole-transporting layer tocomprise two or more sublayers of differing compositions, thecomposition of each sublayer being as described above. The thickness ofthe hole-transporting layer can be between 10 and about 500 nm andsuitably between 50 and 300 nm.

Light-Emitting Layer (LEL)

In addition to the light-emitting materials of this invention,additional light emitting materials may be used in the EL device,including other fluorescent materials. Other fluorescent materials maybe used in the same layer as the boron complex material, in adjacentlayers, in adjacent pixels, or any combination.

As more fully described in U.S. Pat. Nos. 4,769,292 and 5,935,721, thelight-emitting layer (LEL) of the organic EL element includes aluminescent material where electroluminescence is produced as a resultof electron-hole pair recombination. The light-emitting layer can becomprised of a single material, but more commonly consists of a hostmaterial doped with a guest emitting material or materials where lightemission comes primarily from the emitting materials and can be of anycolor. The host materials in the light-emitting layer can be anelectron-transporting material, as defined below, a hole-transportingmaterial, as defined above, or another material or combination ofmaterials that support hole-electron recombination. Fluorescent emittingmaterials are typically incorporated at 0.01 to 10% by weight of thehost material.

The host and emitting materials can be small non-polymeric molecules orpolymeric materials such as polyfluorenes and polyvinylarylenes (e.g.,poly(p-phenylenevinylene), PPV). In the case of polymers, small-moleculeemitting materials can be molecularly dispersed into a polymeric host,or the emitting materials can be added by copolymerizing a minorconstituent into a host polymer. Host materials may be mixed together inorder to improve film formation, electrical properties, light emissionefficiency, operating lifetime, or manufacturability. The host maycomprise a material that has good hole-transporting properties and amaterial that has good electron-transporting properties.

An important relationship for choosing a fluorescent material as a guestemitting material is a comparison of the excited singlet-state energiesof the host and the fluorescent material. It is highly desirable thatthe excited singlet-state energy of the fluorescent material be lowerthan that of the host material. The excited singlet-state energy isdefined as the difference in energy between the emitting singlet stateand the ground state. For non-emissive hosts, the lowest excited stateof the same electronic spin as the ground state is considered theemitting state.

Host and emitting materials known to be of use include, but are notlimited to, those disclosed in U.S. Pat. No. 4,768,292, U.S. Pat. No.5,141,671, U.S. Pat. No. 5,150,006, U.S. Pat. No. 5,151,629, U.S. Pat.No. 5,405,709, U.S. Pat. No. 5,484,922, U.S. Pat. No. 5,593,788, U.S.Pat. No. 5,645,948, U.S. Pat. No. 5,683,823, U.S. Pat. No. 5,755,999,U.S. Pat. No. 5,928,802, U.S. Pat. No. 5,935,720, U.S. Pat. No.5,935,721, and U.S. Pat. No. 6,020,078.

Metal complexes of 8-hydroxyquinoline and similar derivatives, alsoknown as metal-chelated oxinoid compounds (Formula E), constitute oneclass of useful host compounds capable of supportingelectroluminescence, and are particularly suitable for light emission ofwavelengths longer than 500 nm, e.g., green, yellow, orange, and red.

wherein

-   -   M represents a metal;    -   n is an integer of from 1 to 4; and    -   Z independently in each occurrence represents the atoms        completing a nucleus having at least two fused aromatic rings.

From the foregoing it is apparent that the metal can be monovalent,divalent, trivalent, or tetravalent metal. The metal can, for example,be an alkali metal, such as lithium, sodium, or potassium; an alkalineearth metal, such as magnesium or calcium; a trivalent metal, suchaluminum or gallium, or another metal such as zinc or zirconium.Generally any monovalent, divalent, trivalent, or tetravalent metalknown to be a useful chelating metal can be employed.

Z completes a heterocyclic nucleus containing at least two fusedaromatic rings, at least one of which is an azole or azine ring.Additional rings, including both aliphatic and aromatic rings, can befused with the two required rings, if required. To avoid addingmolecular bulk without improving on function the number of ring atoms isusually maintained at 18 or less.

Illustrative of useful chelated oxinoid compounds are the following:

-   -   CO-1: Aluminum trisoxine [alias,        tris(8-quinolinolato)aluminum(III)]    -   CO-2: Magnesium bisoxine [alias,        bis(8-quinolinolato)magnesium(II)]    -   CO-3: Bis[benzo{f}-8-quinolinolato]zinc (II)    -   CO-4:        Bis(2-methyl-8-quinolinolato)aluminum(II)-μ-oxo-bis(2-methyl-8-quinolinolato)        aluminum(III)    -   CO-5: Indium trisoxine [alias, tris(8-quinolinolato)indium]    -   CO-6: Aluminum tris(5-methyloxine) [alias,        tris(5-methyl-8-quinolinolato) aluminum(III)]    -   CO-7: Lithium oxine [alias, (8-quinolinolato)lithium(I)]    -   CO-8: Gallium oxine [alias, tris(8-quinolinolato)gallium(III)]    -   CO-9: Zirconium oxine [alias,        tetra(8-quinolinolato)zirconium(IV)]

Derivatives of 9,10-di-(2-naphthyl)anthracene (Formula F) constitute oneclass of useful host materials capable of supportingelectroluminescence, and are particularly suitable for light emission ofwavelengths longer than 400 nm, e.g., blue, green, yellow, orange orred.

wherein: R¹, R², R³, R⁴, R⁵, and R⁶ represent one or more substituentson each ring where each substituent is individually selected from thefollowing groups:

-   -   Group 1: hydrogen, or alkyl of from 1 to 24 carbon atoms;    -   Group 2: aryl or substituted aryl of from 5 to 20 carbon atoms;    -   Group 3: carbon atoms from 4 to 24 necessary to complete a fused        aromatic ring of anthracenyl; pyrenyl, or perylenyl;    -   Group 4: heteroaryl or substituted heteroaryl of from 5 to 24        carbon atoms as necessary to complete a fused heteroaromatic        ring of furyl, thienyl, pyridyl, quinolinyl or other        heterocyclic systems;    -   Group 5: alkoxylamino, alkylamino, or arylamino of from 1 to 24        carbon atoms; and    -   Group 6: fluorine, chlorine, bromine or cyano.

Illustrative examples include 9,10-di-(2-naphthyl)anthracene and2-t-butyl-9,10-di-(2-naphthyl)anthracene. Other anthracene derivativescan be useful as a host in the LEL, including derivatives of9,10-bis[4-(2,2-diphenylethenyl)phenyl]anthracene.

Benzazole derivatives (Formula G) constitute another class of usefulhost materials capable of supporting electroluminescence, and areparticularly suitable for light emission of wavelengths longer than 400nm, e.g., blue, green, yellow, orange or red.

wherein:

-   -   n is an integer of 3 to 8;    -   Z is O, NR or S; and    -   R and R′ are individually hydrogen; alkyl of from 1 to 24 carbon        atoms, for example, propyl, t-butyl, heptyl, and the like; aryl        or hetero-atom substituted aryl of from 5 to 20 carbon atoms for        example phenyl and naphthyl, furyl, thienyl, pyridyl, quinolinyl        and other heterocyclic systems; or halo such as chloro, fluoro;        or atoms necessary to complete a fused aromatic ring; and

L is a linkage unit consisting of alkyl, aryl, substituted alkyl, orsubstituted aryl, which connects the multiple benzazoles together. L maybe either conjugated with the multiple benzazoles or not in conjugationwith them. An example of a useful benzazole is2,2′,2″-(1,3,5-phenylene)tris[1-phenyl-1H-benzimidazole].

Styrylarylene derivatives as described in U.S. Pat. No. 5,121,029 and JP08333569 are also useful hosts for blue emission. For example,9,10-bis[4-(2,2-diphenylethenyl)phenyl]anthracene and4,4′-bis(2,2-diphenylethenyl)-1,1′-biphenyl (DPVBi) are useful hosts forblue emission.

Useful fluorescent emitting materials include, but are not limited to,derivatives of anthracene, tetracene, xanthene, perylene, rubrene,coumarin, rhodamine, and quinacridone, dicyanomethylenepyran compounds,thiopyran compounds, polymethine compounds, pyrylium and thiapyryliumcompounds, fluorene derivatives, periflanthene derivatives,indenoperylene derivatives, bis(azinyl)amine boron compounds,bis(azinyl)methane compounds, and carbostyryl compounds. Illustrativeexamples of useful materials include, but are not limited to, thefollowing:

X R1 R2 L9 O H H L10 O H Methyl L11 O Methyl H L12 O Methyl Methyl L13 OH t-butyl L14 O t-butyl H L15 O t-butyl t-butyl L16 S H H L17 S H MethylL18 S Methyl H L19 S Methyl Methyl L20 S H t-butyl L21 S t-butyl H L22 St-butyl t-butyl

X R1 R2 L23 O H H L24 O H Methyl L25 O Methyl H L26 O Methyl Methyl L27O H t-butyl L28 O t-butyl H L29 O t-butyl t-butyl L30 S H H L31 S HMethyl L32 S Methyl H L33 S Methyl Methyl L34 S H t-butyl L35 S t-butylH L36 S t-butyl t-butyl

R L37 phenyl L38 methyl L39 t-butyl L40 mesityl

R L41 phenyl L42 methyl L43 t-butyl L44 mesityl

In addition to the light-emitting materials of this invention,light-emitting phosphorescent materials may be used in the EL device.For convenience, the phosphorescent complex guest material may bereferred to herein as a phosphorescent material. The phosphorescentmaterial typically includes one or more ligands, for example monoanionicligands that can be coordinated to a metal through an sp² carbon and aheteroatom. Conveniently, the ligand can be phenylpyridine (ppy) orderivatives or analogs thereof. Examples of some useful phosphorescentorganometallic materials includetris(2-phenylpyridinato-N,C^(2′))iridium(III),bis(2-phenylpyridinato-N,C²)iridium(III)(acetylacetonate), andbis(2-phenylpyridinato-N,C^(2′))platinum(II). Usefully, manyphosphorescent organometallic materials emit in the green region of thespectrum, that is, with a maximum emission in the range of 510 to 570nm.

Phosphorescent materials may be used singly or in combinations otherphosphorescent materials, either in the same or different layers.Phosphorescent materials and suitable hosts are described in WO00/57676, WO 00/70655, WO 01/41512 A1, WO 02/15645 A1, US 2003/0017361A1, WO 01/93642 A1, WO 01/39234 A2, U.S. Pat. No. 6,458,475 B1, WO02/071813 A1, U.S. Pat. No. 6,573,651 B2, US 2002/0197511 A1, WO02/074015 A2, U.S. Pat. No. 6,451,455 B1, US 2003/0072964 A1, US2003/0068528 A1, U.S. Pat. No. 6,413,656 B1, U.S. Pat. No. 6,515,298 B2,U.S. Pat. No. 6,451,415 B1, U.S. Pat. No. 6,097,147, US 2003/0124381 A1,US 2003/0059646 A1, US 2003/0054198 A1, EP 1 239 526 A2, EP 1 238 981A2, EP 1 244 155 A2, US 2002/0100906 A1, US 2003/0068526 A1, US2003/0068535 A1, JP 2003073387A, JP 2003 073388A, US 2003/0141809 A1, US2003/0040627 A1, JP 2003059667A, JP 2003073665A, and US 2002/0121638 A1.

The emission wavelengths of cyclometallated Ir(III) complexes of thetype IrL₃ and IrL₂L′, such as the green-emittingfac-tris(2-phenylpyridinato-N,C^(2′))iridium(III) andbis(2-phenylpyridinato-N,C^(2′))iridium(III)(acetylacetonate) may beshifted by substitution of electron donating or withdrawing groups atappropriate positions on the cyclometallating ligand L, or by choice ofdifferent heterocycles for the cyclometallating ligand L. The emissionwavelengths may also be shifted by choice of the ancillary ligand L′.Examples of red emitters are thebis(2-(2′-benzothienyl)pyridinato-N,C^(3′))iridium(III)(acetylacetonate)and tris(2-phenylisoquinolinato-N,C)iridium(III). A blue-emittingexample isbis(2-(4,6-difluorophenyl)-pyridinato-N,C^(2′))iridium(III)(picolinate).

Red electrophosphorescence has been reported, usingbis(2-(2′-benzo[4,5-a]thienyl)pyridinato-N, C³) iridium(acetylacetonate) [Btp₂Ir(acac)] as the phosphorescent material (C.Adachi, S. Lamansky, M. A. Baldo, R. C. Kwong, M. E. Thompson, and S. R.Forrest, App. Phys. Lett., 78, 1622–1624 (2001)).

Other important phosphorescent materials include cyclometallated Pt(II)complexes such as cis-bis(2-phenylpyridinato-N,C^(2′))platinum(II),cis-bis(2-(2′-thienyl)pyridinato-N,C^(3′)) platinum(II),cis-bis(2-(2′-thienyl)quinolinato-N,C^(5′)) platinum(II), or(2-(4,6-difluorophenyl)pyridinato-N,C²′) platinum (II)(acetylacetonate). Pt (II) porphyrin complexes such as2,3,7,8,12,13,17,18-octaethyl-21H, 23H-porphine platinum(II) are alsouseful phosphorescent materials.

Still other examples of useful phosphorescent materials includecoordination complexes of the trivalent lanthanides such as Tb³⁺ andEu³⁺ (J. Kido et al., Appl. Phys. Lett., 65, 2124 (1994)).

Suitable host materials for phosphorescent materials should be selectedso that transfer of a triplet exciton can occur efficiently from thehost material to the phosphorescent material but cannot occurefficiently from the phosphorescent material to the host material.Therefore, it is highly desirable that the triplet energy of thephosphorescent material be lower than the triplet energy of the host.Generally speaking, a large triplet energy implies a large opticalbandgap. However, the band gap of the host should not be chosen so largeas to cause an unacceptable barrier to injection of charge carriers intothe light-emitting layer and an unacceptable increase in the drivevoltage of the OLED. Suitable host materials are described in WO00/70655 A2; 01/39234 A2; 01/93642 A1; 02/074015 A2; 02/15645 A1, and US20020117662. Suitable hosts include certain aryl amines, triazoles,indoles and carbazole compounds. Examples of desirable hosts are4,4′-N,N′-dicarbazole-biphenyl, otherwise known as4,4′-bis(carbazol-9-yl)biphenyl or CBP;4,4′-N,N′-dicarbazole-2,2′-dimethyl-biphenyl, otherwise known as2,2′-dimethyl4,4′-bis(carbazol-9-yl)biphenyl or CDBP;1,3-bis(N,N′-dicarbazole)benzene, otherwise known as1,3-bis(carbazol-9-yl)benzene, and poly(N-vinylcarbazole), includingtheir derivatives.

Desirable host materials are capable of forming a continuous film.

Hole-Blocking Layer (HBL)

In addition to suitable hosts, an OLED device employing a phosphorescentmaterial often requires at least one hole-blocking layer placed betweenthe electron-transporting layer 111 and the light-emitting layer 109 tohelp confine the excitons and recombination events to the light-emittinglayer comprising the host and phosphorescent material. In this case,there should be an energy barrier for hole migration from the host intothe hole-blocking layer, while electrons should pass readily from thehole-blocking layer into the light-emitting layer comprising a host anda phosphorescent material. The first requirement entails that theionization potential of the hole-blocking layer be larger than that ofthe light-emitting layer 109, desirably by 0.2 eV or more. The secondrequirement entails that the electron affinity of the hole-blockinglayer not greatly exceed that of the light-emitting layer 109, anddesirably be either less than that of light-emitting layer or not exceedthat of the light-emitting layer by more than about 0.2 eV.

When used with an electron-transporting layer whose characteristicluminescence is green, such as an Alq-containing electron-transportinglayer as described below, the requirements concerning the energies ofthe highest occupied molecular orbital (HOMO) and lowest unoccupiedmolecular orbital (LUMO) of the material of the hole-blocking layerfrequently result in a characteristic luminescence of the hole-blockinglayer at shorter wavelengths than that of the electron-transportinglayer, such as blue, violet, or ultraviolet luminescence. Thus, it isdesirable that the characteristic luminescence of the material of ahole-blocking layer be blue, violet, or ultraviolet. It is furtherdesirable, but not absolutely required, that the triplet energy of thehole-blocking material be greater than that of the phosphorescentmaterial. Suitable hole-blocking materials are described in WO00/70655A2 and WO 01/93642 A1. Two examples of useful hole-blockingmaterials are bathocuproine (BCP) andbis(2-methyl-8-quinolinolato)(4-phenylphenolato)aluminum(III) (BAlq).The characteristic luminescence of BCP is in the ultraviolet, and thatof BAlq is blue. Metal complexes other than BAlq are also known to blockholes and excitons as described in US 20030068528. In addition, US20030175553 A1 describes the use offac-tris(1-phenylpyrazolato-N,C^(2′))iridium(III) (Irppz) for thispurpose.

When a hole-blocking layer is used, its thickness can be between 2 and100 nm and suitably between 5 and 10 nm.

Electron-Transporting Layer (ETL)

Desirable thin film-forming materials for use in forming theelectron-transporting layer 111 of the organic EL devices of thisinvention are metal-chelated oxinoid compounds, including chelates ofoxine itself (also commonly referred to as 8-quinolinol or8-hydroxyquinoline). Such compounds help to inject and transportelectrons, exhibit high levels of performance, and are readilyfabricated in the form of thin films. Exemplary of contemplated oxinoidcompounds are those satisfying structural formula (E), previouslydescribed.

Other electron-transporting materials suitable for use in theelectron-transporting layer 111 include various butadiene derivatives asdisclosed in U.S. Pat. No. 4,356,429 and various heterocyclic opticalbrighteners as described in U.S. Pat. No. 4,539,507. Benzazolessatisfying structural formula (G) are also useful electron transportingmaterials. Triazines are also known to be useful as electrontransporting materials.

If both a hole-blocking layer and an electron-transporting layer 111 areused, electrons should pass readily from the electron-transporting layer111 into the hole-blocking layer. Therefore, the electron affinity ofthe electron-transporting layer 111 should not greatly exceed that ofthe hole-blocking layer. Desirably, the electron affinity of theelectron-transporting layer should be less than that of thehole-blocking layer or not exceed it by more than about 0.2 eV.

If an electron-transporting layer is used, its thickness may be between2 and 100 nm and suitably between 5 and 20 nm.

Other Useful Organic Layers and Device Architecture

In some instances, layers 109 through 111 can optionally be collapsedinto a single layer that serves the function of supporting both lightemission and electron transportation. The hole-blocking layer, whenpresent, and layer 111 may also be collapsed into a single layer thatfunctions to block holes or excitons, and supports electron transport.It also known in the art that emitting materials may be included in thehole-transporting layer 107. In that case, the hole-transportingmaterial may serve as a host. Multiple materials may be added to one ormore layers in order to create a white-emitting OLED, for example, bycombining blue- and yellow-emitting materials, cyan- and red-emittingmaterials, or red-, green-, and blue-emitting materials. White-emittingdevices are described, for example, in EP 1 187 235, US 20020025419, EP1 182 244, U.S. Pat. No. 5,683,823, U.S. Pat. No. 5,503,910, U.S. Pat.No. 5,405,709, and U.S. Pat. No. 5,283,182 and can be equipped with asuitable filter arrangement to produce a color emission.

This invention may be used in so-called stacked device architecture, forexample, as taught in U.S. Pat. No. 5,703,436 and U.S. Pat. No.6,337,492.

Deposition of Organic Layers

The organic materials mentioned above are suitably deposited by anymeans suitable for the form of the organic materials. In the case ofsmall molecules, they are conveniently deposited through sublimation orevaporation, but can be deposited by other means such as coating from asolvent together with an optional binder to improve film formation. Ifthe material is a polymer, solvent deposition is usually preferred. Thematerial to be deposited by sublimation or evaporation can be vaporizedfrom a sublimator “boat” often comprised of a tantalum material, e.g.,as described in U.S. Pat. No. 6,237,529, or can be first coated onto adonor sheet and then sublimed in closer proximity to the substrate.Layers with a mixture of materials can utilize separate sublimator boatsor the materials can be pre-mixed and coated from a single boat or donorsheet. Patterned deposition can be achieved using shadow masks, integralshadow masks (U.S. Pat. No. 5,294,870), spatially-defined thermal dyetransfer from a donor sheet (U.S. Pat. No. 5,688,551, U.S. Pat. No.5,851,709 and U.S. Pat. No. 6,066,357) or an inkjet method (U.S. Pat.No. 6,066,357).

Encapsulation

Most OLED devices are sensitive to moisture or oxygen, or both, so theyare commonly sealed in an inert atmosphere such as nitrogen or argon,along with a desiccant such as alumina, bauxite, calcium sulfate, clays,silica gel, zeolites, alkaline metal oxides, alkaline earth metaloxides, sulfates, or metal halides and perchlorates. Methods forencapsulation and desiccation include, but are not limited to, thosedescribed in U.S. Pat. No. 6,226,890. In addition, barrier layers suchas SiO_(x), Teflon, and alternating inorganic/polymeric layers are knownin the art for encapsulation. Any of these methods of sealing orencapsulation and desiccation can be used with the EL devicesconstructed according to the present invention.

Optical Optimization

OLED devices of this invention can employ various well-known opticaleffects in order to enhance their emissive properties if desired. Thisincludes optimizing layer thicknesses to yield maximum lighttransmission, providing dielectric mirror structures, replacingreflective electrodes with light-absorbing electrodes, providinganti-glare or anti-reflection coatings over the display, providing apolarizing medium over the display, or providing colored, neutraldensity, or color-conversion filters over the display. Filters,polarizers, and anti-glare or anti-reflection coatings may bespecifically provided over the EL device or as part of the EL device.

Embodiments of the invention can provide advantageous features such ashigher luminous yield, lower drive voltage, and higher power efficiency,or reduced sublimation temperatures. Embodiments of the compounds usefulin the invention can provide a wide range of hues including those usefulin the emission of white light (directly or through filters to providemulticolor displays). Embodiments of the invention can also provide anarea lighting device.

The invention and its advantages can be better appreciated by thefollowing examples. Unless otherwise specifically stated, use of theterm “substituted” or “substituent” means any group or atom other thanhydrogen. Additionally, when the term “group” is used, it means thatwhen a substituent group contains a substitutable hydrogen, it is alsointended to encompass not only the substituent's unsubstituted form, butalso its form further substituted with any substituent group or groupsas herein mentioned, so long as the substituent does not destroyproperties necessary for device utility. Suitably, a substituent groupmay be halogen or may be bonded to the remainder of the molecule by anatom of carbon, silicon, oxygen, nitrogen, phosphorous, sulfur,selenium, or boron. The substituent may be, for example, halogen, suchas chloro, bromo or fluoro; nitro; hydroxyl; cyano; carboxyl; or groupswhich may be further substituted, such as alkyl, including straight orbranched chain or cyclic alkyl, such as methyl, trifluoromethyl, ethyl,t-butyl, 3-(2,4-di-t-pentylphenoxy) propyl, and tetradecyl; alkenyl,such as ethylene, 2-butene; alkoxy, such as methoxy, ethoxy, propoxy,butoxy, 2-methoxyethoxy, sec-butoxy, hexyloxy, 2-ethylhexyloxy,tetradecyloxy, 2-(2,4-di-t-pentylphenoxy)ethoxy, and 2-dodecyloxyethoxy;aryl such as phenyl, 4-t-butylphenyl, 2,4,6-trimethylphenyl, naphthyl;aryloxy, such as phenoxy, 2-methylphenoxy, alpha- or beta-naphthyloxy,and 4-tolyloxy; carbonamido, such as acetamido, benzamido, butyramido,tetradecanamido, alpha-(2,4-di-t-pentylphenoxy)acetamido,alpha-(2,4-di-t-pentylphenoxy)butyramido,alpha-(3-pentadecylphenoxy)-hexanamido,alpha-(4-hydroxy-3-t-butylphenoxy)-tetradecanamido,2-oxo-pyrrolidin-1-yl, 2-oxo-5-tetradecylpyrrolin-1-yl,N-methyltetradecanamido, N-succinimido, N-phthalimido,2,5-dioxo-1-oxazolidinyl, 3-dodecyl-2,5-dioxo-1-imidazolyl, andN-acetyl-N-dodecylamino, ethoxycarbonylamino, phenoxycarbonylamino,benzyloxycarbonylamino, hexadecyloxycarbonylamino,2,4-di-t-butylphenoxycarbonylamino, phenylcarbonylamino,2,5-(di-t-pentylphenyl)carbonylamino, p-dodecylphenylcarbonylamino,p-tolylcarbonylamino, N-methylureido, N,N-dimethylureido,N-methyl-N-dodecylureido, N-hexadecylureido, N,N-dioctadecylureido,N,N-dioctyl-N′-ethylureido, N-phenylureido, N,N-diphenylureido,N-phenyl-N-p-tolylureido, N-(m-hexadecylphenyl)ureido,N,N-(2,5-di-t-pentylphenyl)-N′-ethylureido, and t-butylcarbonamido;sulfonamido, such as methylsulfonamido, benzenesulfonamido,p-tolylsulfonamido, p-dodecylbenzenesulfonamido,N-methyltetradecylsulfonamido, N,N-dipropylsulfamoylamino, andhexadecylsulfonamido; sulfamoyl, such as N-methylsulfamoyl,N-ethylsulfamoyl, N,N-dipropylsulfamoyl, N-hexadecylsulfamoyl,N,N-dimethylsulfamoyl, N-[3-(dodecyloxy)propyl]sulfamoyl,N-[4-(2,4-di-t-pentylphenoxy)butyl]sulfamoyl,N-methyl-N-tetradecylsulfamoyl, and N-dodecylsulfamoyl; carbamoyl, suchas N-methylcarbamoyl, N,N-dibutylcarbamoyl, N-octadecylcarbamoyl,N-[4-(2,4-di-t-pentylphenoxy)butyl]carbamoyl,N-methyl-N-tetradecylcarbamoyl, and N,N-dioctylcarbamoyl; acyl, such asacetyl, (2,4-di-t-amylphenoxy)acetyl, phenoxycarbonyl,p-dodecyloxyphenoxycarbonyl methoxycarbonyl, butoxycarbonyl,tetradecyloxycarbonyl, ethoxycarbonyl, benzyloxycarbonyl,3-pentadecyloxycarbonyl, and dodecyloxycarbonyl; sulfonyl, such asmethoxysulfonyl, octyloxysulfonyl, tetradecyloxysulfonyl,2-ethylhexyloxysulfonyl, phenoxysulfonyl,2,4-di-t-pentylphenoxysulfonyl, methylsulfonyl, octylsulfonyl,2-ethylhexylsulfonyl, dodecylsulfonyl, hexadecylsulfonyl,phenylsulfonyl, 4-nonylphenylsulfonyl, and p-tolylsulfonyl; sulfonyloxy,such as dodecylsulfonyloxy, and hexadecylsulfonyloxy; sulfinyl, such asmethylsulfinyl, octylsulfinyl, 2-ethylhexylsulfinyl, dodecylsulfinyl,hexadecylsulfinyl, phenylsulfinyl, 4-nonylphenylsulfinyl, andp-tolylsulfinyl; thio, such as ethylthio, octylthio, benzylthio,tetradecylthio, 2-(2,4-di-t-pentylphenoxy)ethylthio, phenylthio,2-butoxy-5-t-octylphenylthio, and p-tolylthio; acyloxy, such asacetyloxy, benzoyloxy, octadecanoyloxy, p-dodecylamidobenzoyloxy,N-phenylcarbamoyloxy, N-ethylcarbamoyloxy, and cyclohexylcarbonyloxy;amine, such as phenylanilino, 2-chloroanilino, diethylamine,dodecylamine; imino, such as 1 (N-phenylimido)ethyl, N-succinimido or3-benzylhydantoinyl; phosphate, such as dimethylphosphate andethylbutylphosphate; phosphite, such as diethyl and dihexylphosphite; aheterocyclic group, a heterocyclic oxy group or a heterocyclic thiogroup, each of which may be substituted and which contain a 3 to 7membered heterocyclic ring composed of carbon atoms and at least onehetero atom selected from the group consisting of oxygen, nitrogen,sulfur, phosphorous, or boron, such as 2-furyl, 2-thienyl,2-benzimidazolyloxy or 2-benzothiazolyl; quaternary ammonium, such astriethylammonium; quaternary phosphonium, such as triphenylphosphonium;and silyloxy, such as trimethylsilyloxy.

If desired, the substituents may themselves be further substituted oneor more times with the described substituent groups. The particularsubstituents used may be selected by those skilled in the art to attainthe desired desirable properties for a specific application and caninclude, for example, electron-withdrawing groups, electron-donatinggroups, and steric groups. When a molecule may have two or moresubstituents, the substituents may be joined together to form a ringsuch as a fused ring unless otherwise provided. Generally, the abovegroups and substituents thereof may include those having up to 48 carbonatoms, typically 1 to 36 carbon atoms and usually less than 24 carbonatoms, but greater numbers are possible depending on the particularsubstituents selected.

General Device Architecture

The present invention can be employed in many EL device configurationsusing small molecule materials, oligomeric materials, polymericmaterials, or combinations thereof. These include very simple structurescomprising a single anode and cathode to more complex devices, such aspassive matrix displays comprised of orthogonal arrays of anodes andcathodes to form pixels, and active-matrix displays where each pixel iscontrolled independently, for example, with thin film transistors(TFTs).

There are numerous configurations of the organic layers wherein thepresent invention can be successfully practiced. The essentialrequirements of an OLED are an anode, a cathode, and an organiclight-emitting layer located between the anode and cathode. Additionallayers may be employed as more fully described hereafter.

A typical structure according to the present invention and especiallyuseful for a small molecule device, is shown in FIG. 1 and is comprisedof a substrate 101, an anode 103, a hole-injecting layer 105, ahole-transporting layer 107, a light-emitting layer 109, anelectron-transporting layer 111, and a cathode 113. These layers aredescribed in detail below. Note that the substrate 101 may alternativelybe located adjacent to the cathode 113, or the substrate 101 mayactually constitute the anode 103 or cathode 113. The organic layersbetween the anode 103 and cathode 113 are conveniently referred to asthe organic EL element. Also, the total combined thickness of theorganic layers is desirably less than 500 nm. If the device includesphosphorescent material, a hole-blocking layer, located between thelight-emitting layer and the electron-transporting layer, may bepresent.

The anode 103 and cathode 113 of the OLED are connected to avoltage/current source through electrical conductors. The OLED isoperated by applying a potential between the anode 103 and cathode 113such that the anode 103 is at a more positive potential than the cathode113. Holes are injected into the organic EL element from the anode 103and electrons are injected into the organic EL element at the cathode113. Enhanced device stability can sometimes be achieved when the OLEDis operated in an AC mode where, for some time period in the AC cycle,the potential bias is reversed and no current flows. An example of an ACdriven OLED is described in U.S. Pat. No. 5,552,678.

Substrate

The OLED device of this invention is typically provided over asupporting substrate 101 where either the cathode 113 or anode 103 canbe in contact with the substrate. The electrode in contact with thesubstrate 101 is conveniently referred to as the bottom electrode.Conventionally, the bottom electrode is the anode 103, but thisinvention is not limited to that configuration. The substrate 101 caneither be light transmissive or opaque, depending on the intendeddirection of light emission. The light transmissive property isdesirable for viewing the EL emission through the substrate 101.Transparent glass or plastic is commonly employed in such cases. Thesubstrate 101 can be a complex structure comprising multiple layers ofmaterials. This is typically the case for active matrix substrateswherein TFTs are provided below the OLED layers. It is still necessarythat the substrate 101, at least in the emissive pixelated areas, becomprised of largely transparent materials such as glass or polymers.For applications where the EL emission is viewed through the topelectrode, the transmissive characteristic of the bottom support isimmaterial, and therefore the substrate can be light transmissive, lightabsorbing or light reflective. Substrates for use in this case include,but are not limited to, glass, plastic, semiconductor materials such assilicon, ceramics, and circuit board materials. Again, the substrate 101can be a complex structure comprising multiple layers of materials suchas found in active matrix TFT designs. It is necessary to provide inthese device configurations a light-transparent top electrode.

Anode

When the desired electroluminescent light emission (EL) is viewedthrough the anode, the anode 103 should be transparent or substantiallytransparent to the emission of interest. Common transparent anodematerials used in this invention are indium-tin oxide (ITO), indium-zincoxide (IZO) and tin oxide, but other metal oxides can work including,but not limited to, aluminum- or indium-doped zinc oxide,magnesium-indium oxide, and nickel-tungsten oxide. In addition to theseoxides, metal nitrides, such as gallium nitride, and metal selenides,such as zinc selenide, and metal sulfides, such as zinc sulfide, can beused as the anode 103. For applications where EL emission is viewed onlythrough the cathode 113, the transmissive characteristics of the anode103 are immaterial and any conductive material can be used, transparent,opaque or reflective. Example conductors for this application include,but are not limited to, gold, iridium, molybdenum, palladium, andplatinum. Typical anode materials, transmissive or otherwise, have awork function of 4.1 eV or greater. Desired anode materials are commonlydeposited by any suitable means such as evaporation, sputtering,chemical vapor deposition, or electrochemical means. Anodes can bepatterned using well-known photolithographic processes. Optionally,anodes may be polished prior to application of other layers to reducesurface roughness so as to minimize short circuits or enhancereflectivity.

Cathode

When light emission is viewed solely through the anode 103, the cathode113 used in this invention can be comprised of nearly any conductivematerial. Desirable materials have good film-forming properties toensure good contact with the underlying organic layer, promote electroninjection at low voltage, and have good stability. Useful cathodematerials often contain a low work function metal (<4.0 eV) or metalalloy. One useful cathode material is comprised of a Mg:Ag alloy whereinthe percentage of silver is in the range of 1 to 20%, as described inU.S. Pat. No. 4,885,221. Another suitable class of cathode materialsincludes bilayers comprising the cathode and a thin electron-injectionlayer (EIL) in contact with an organic layer (e.g., an electrontransporting layer (ETL)), the cathode being capped with a thicker layerof a conductive metal. Here, the EIL preferably includes a low workfunction metal or metal salt, and if so, the thicker capping layer doesnot need to have a low work function. One such cathode is comprised of athin layer of LiF followed by a thicker layer of Al as described in U.S.Pat. No. 5,677,572. An ETL material doped with an alkali metal, forexample, Li-doped Alq, is another example of a useful EIL. Other usefulcathode material sets include, but are not limited to, those disclosedin U.S. Pat. Nos. 5,059,861, 5,059,862, and 6,140,763.

When light emission is viewed through the cathode, the cathode 113 mustbe transparent or nearly transparent. For such applications, metals mustbe thin or one must use transparent conductive oxides, or a combinationof these materials. Optically transparent cathodes have been describedin more detail in U.S. Pat. No. 4,885,211, U.S. Pat. No. 5,247,190, JP3,234,963, U.S. Pat. No. 5,703,436, U.S. Pat. No. 5,608,287, U.S. Pat.No. 5,837,391, U.S. Pat. No. 5,677,572, U.S. Pat. No. 5,776,622, U.S.Pat. No. 5,776,623, U.S. Pat. No. 5,714,838, U.S. Pat. No. 5,969,474,U.S. Pat. No. 5,739,545, U.S. Pat. No. 5,981,306, U.S. Pat. No.6,137,223, U.S. Pat. No. 6,140,763, U.S. Pat. No. 6,172,459, EP 1 076368, U.S. Pat. No. 6,278,236, and U.S. Pat. No. 6,284,3936. Cathodematerials are typically deposited by any suitable method such asevaporation, sputtering, or chemical vapor deposition. When needed,patterning can be achieved through many well known methods including,but not limited to, through-mask deposition, integral shadow masking asdescribed in U.S. Pat. No. 5,276,380 and EP 0 732 868, laser ablation,and selective chemical vapor deposition.

Hole-Injecting Layer (HIL)

A hole-injecting layer 105 may be provided between anode 103 andhole-transporting layer 107. The hole-injecting layer can serve toimprove the film formation property of subsequent organic layers and tofacilitate injection of holes into the hole-transporting layer 107.Suitable materials for use in the hole-injecting layer 105 include, butare not limited to, porphyrinic compounds as described in U.S. Pat. No.4,720,432, plasma-deposited fluorocarbon polymers as described in U.S.Pat. No. 6,208,075, and some aromatic amines, for example, MTDATA(4,4′,4″-tris[(3-methylphenyl)phenylamino]triphenylamine). Alternativehole-injecting materials reportedly useful in organic EL devices aredescribed in EP 0 891 121 A1 and EP 1 029 909 A1. A hole-injection layeris conveniently used in the present invention, and is desirably aplasma-deposited fluorocarbon polymer. The thickness of a hole-injectionlayer containing a plasma-deposited fluorocarbon polymer can be in therange of 0.2 nm to 15 nm and suitably in the range of 0.3 to 1.5 nm.

Hole-Transporting Layer (HTL)

While not always necessary, it is often useful to include ahole-transporting layer in an OLED device. The hole-transporting layer107 of the organic EL device contains at least one hole-transportingcompound such as an aromatic tertiary amine, where the latter isunderstood to be a compound containing at least one trivalent nitrogenatom that is bonded only to carbon atoms, at least one of which is amember of an aromatic ring. In one form the aromatic tertiary amine canbe an arylamine, such as a monoarylamine, diarylamine, triarylamine, ora polymeric arylamine. Exemplary monomeric triarylamines are illustratedby Klupfel et al. U.S. Pat. No. 3,180,730. Other suitable triarylaminessubstituted with one or more vinyl radicals and/or comprising at leastone active hydrogen containing group are disclosed by Brantley et alU.S. Pat. No. 3,567,450 and U.S. Pat. No. 3,658,520.

A more preferred class of aromatic tertiary amines is those whichinclude at least two aromatic tertiary amine moieties as described inU.S. Pat. No. 4,720,432 and U.S. Pat. No. 5,061,569. Such compoundsinclude those represented by structural formula (A).

wherein Q₁ and Q₂ are independently selected aromatic tertiary aminemoieties and G is a linking group such as an arylene, cycloalkylene, oralkylene group of a carbon to carbon bond. In one embodiment, at leastone of Q₁ or Q₂ contains a polycyclic fused ring structure, e.g., anaphthalene. When G is an aryl group, it is conveniently a phenylene,biphenylene, or naphthalene moiety.

A useful class of triarylamines satisfying structural formula (A) andcontaining two triarylamine moieties is represented by structuralformula (B):

where

-   -   R₁ and R₂ each independently represents a hydrogen atom, an aryl        group, or an alkyl group or R₁ and R₂ together represent the        atoms completing a cycloalkyl group; and    -   R₃ and R₄ each independently represents an aryl group, which is        in turn substituted with a diaryl substituted amino group, as        indicated by structural formula (C):

wherein R₅ and R₆ are independently selected aryl groups. In oneembodiment, at least one of R₅ or R₆ contains a polycyclic fused ringstructure, e.g., a naphthalene.

Another class of aromatic tertiary amines is the tetraaryldiamines.Desirable tetraaryldiamines include two diarylamino groups, such asindicated by formula (C), linked through an arylene group. Usefultetraaryldiamines include those represented by formula (D).

wherein

-   -   each Are is an independently selected arylene group, such as a        phenylene or anthracene moiety,    -   n is an integer of from 1 to 4, and    -   Ar, R₇, R₈, and R₉ are independently selected aryl groups.

In a typical embodiment, at least one of Ar, R₇, R₈, and R₉ is apolycyclic fused ring structure, e.g., a naphthalene.

The various alkyl, alkylene, aryl, and arylene moieties of the foregoingstructural formulae (A), (B), (C), (D), can each in turn be substituted.Typical substituents include alkyl groups, alkoxy groups, aryl groups,aryloxy groups, and halide such as fluoride, chloride, and bromide. Thevarious alkyl and alkylene moieties typically contain from about 1 to 6carbon atoms. The cycloalkyl moieties can contain from 3 to about 10carbon atoms, but typically contain five, six, or seven ring carbonatoms—e.g., cyclopentyl, cyclohexyl, and cycloheptyl ring structures.The aryl and arylene moieties are usually phenyl and phenylene moieties.

The hole-transporting layer can be formed of a single tertiary aminecompound or a mixture of such compounds. Specifically, one may employ atriarylamine, such as a triarylamine satisfying the formula (B), incombination with a tetraaryldiamine, such as indicated by formula (D).Illustrative of useful aromatic tertiary amines are the following:

-   -   1,1-Bis(4-di-p-tolylaminophenyl)cyclohexane (TAPC)    -   1,1-Bis(4-di-p-tolylaminophenyl)-4-methylcyclohexane    -   1,1-Bis(4-di-p-tolylaminophenyl)-4-phenylcyclohexane    -   1,1-Bis(4-di-p-tolylaminophenyl)-3-phenylpropane (TAPPP)    -   N,N,N′,N′-tetraphenyl-4,4′″-diamino-1,1′:4′,1″:4″,1′″-quaterphenyl    -   Bis(4-dimethylamino-2-methylphenyl)phenylmethane    -   1,4-bis[2-[4-[N,N-di(p-toly)amino]phenyl]vinyl]benzene (BDTAPVB)    -   N,N,N′,N′-Tetra-p-tolyl-4,4′-diaminobiphenyl (TTB)    -   N,N,N′,N′-Tetraphenyl-4,4′-diaminobiphenyl    -   N,N,N′,N′-tetra-1-naphthyl-4,4′-diaminobiphenyl    -   N,N,N′,N′-tetra-2-naphthyl-4,4′-diaminobiphenyl    -   N-Phenylcarbazole    -   4,4′-Bis[N-(1-naphthyl)-N-phenylamino]biphenyl (NPB)    -   4,4′-Bis[N-(1-naphthyl)-N-(2-naphthyl)amino]biphenyl (TNB)    -   4,4′-Bis[N-(1-naphthyl)-N-phenylamino]p-terphenyl    -   4,4′-Bis[N-(2-naphthyl)-N-phenylamino]biphenyl    -   4,4′-Bis[N-(3-acenaphthenyl)-N-phenylamino]biphenyl    -   1,5-Bis[N-(1-naphthyl)-N-phenylamino]naphthalene    -   4,4′-Bis[N-(9-anthryl)-N-phenylamino]biphenyl    -   4,4′-Bis[N-(1-anthryl)-N-phenylamino]-p-terphenyl    -   4,4′-Bis[N-(2-phenanthryl)-N-phenylamino]biphenyl    -   4,4′-Bis[N-(8-fluoranthenyl)-N-phenylamino]biphenyl    -   4,4′-Bis[N-(2-pyrenyl)-N-phenylamino]biphenyl    -   4,4′-Bis[N-(2-naphthacenyl)-N-phenylamino]biphenyl    -   4,4′-Bis[N-(2-perylenyl)-N-phenylamino]biphenyl    -   4,4′-Bis[N-(1-coronenyl)-N-phenylamino]biphenyl    -   2,6-Bis(di-p-tolylamino)naphthalene    -   2,6-Bis[di-(1-naphthyl)amino]naphthalene    -   2,6-Bis[N-(1-naphthyl)-N-(2-naphthyl)amino]naphthalene    -   N,N,N′,N′-Tetra(2-naphthyl)-4,4″-diamino-p-terphenyl    -   4,4′-Bis {N-phenyl-N-[4-(1-naphthyl)-phenyl]amino}biphenyl    -   2,6-Bis[N,N-di(2-naphthyl)amino]fluorene    -   4,4′,4″-tris[(3-methylphenyl)phenylamino]triphenylamine (MTDATA)    -   4,4′-Bis[N-(3-methylphenyl)-N-phenylamino]biphenyl (TPD)

Another class of useful hole-transporting materials includes polycyclicaromatic compounds as described in EP 1 009 041. Tertiary aromaticamines with more than two amine groups may be used including oligomericmaterials. In addition, polymeric hole-transporting materials can beused such as poly(N-vinylcarbazole) (PVK), polythiophenes, polypyrrole,polyaniline, and copolymers such aspoly(3,4-ethylenedioxythiophene)/poly(4-styrenesulfonate) also calledPEDOT/PSS. It is also possible for the hole-transporting layer tocomprise two or more sublayers of differing compositions, thecomposition of each sublayer being as described above. The thickness ofthe hole-transporting layer can be between 10 and about 500 nm andsuitably between 50 and 300 nm.

Light-Emitting Layer (LEL)

In addition to the light-emitting materials of this invention,additional light emitting materials may be used in the EL device,including other fluorescent materials. Other fluorescent materials maybe used in the same layer as the boron complex material, in adjacentlayers, in adjacent pixels, or any combination.

As more fully described in U.S. Pat. Nos. 4,769,292 and 5,935,721, thelight-emitting layer (LEL) of the organic EL element includes aluminescent material where electroluminescence is produced as a resultof electron-hole pair recombination. The light-emitting layer can becomprised of a single material, but more commonly consists of a hostmaterial doped with a guest emitting material or materials where lightemission comes primarily from the emitting materials and can be of anycolor. The host materials in the light-emitting layer can be anelectron-transporting material, as defined below, a hole-transportingmaterial, as defined above, or another material or combination ofmaterials that support hole-electron recombination. Fluorescent emittingmaterials are typically incorporated at 0.01 to 10% by weight of thehost material.

The host and emitting materials can be small non-polymeric molecules orpolymeric materials such as polyfluorenes and polyvinylarylenes (e.g.,poly(p-phenylenevinylene), PPV). In the case of polymers, small-moleculeemitting materials can be molecularly dispersed into a polymeric host,or the emitting materials can be added by copolymerizing a minorconstituent into a host polymer. Host materials may be mixed together inorder to improve film formation, electrical properties, light emissionefficiency, operating lifetime, or manufacturability. The host maycomprise a material that has good hole-transporting properties and amaterial that has good electron-transporting properties.

An important relationship for choosing a fluorescent material as a guestemitting material is a comparison of the excited singlet-state energiesof the host and the fluorescent material. It is highly desirable thatthe excited singlet-state energy of the fluorescent material be lowerthan that of the host material. The excited singlet-state energy isdefined as the difference in energy between the emitting singlet stateand the ground state. For non-emissive hosts, the lowest excited stateof the same electronic spin as the ground state is considered theemitting state.

Host and emitting materials known to be of use include, but are notlimited to, those disclosed in U.S. Pat. No. 4,768,292, U.S. Pat. No.5,141,671, U.S. Pat. No. 5,150,006, U.S. Pat. No. 5,151,629, U.S. Pat.No. 5,405,709, U.S. Pat. No. 5,484,922, U.S. Pat. No. 5,593,788, U.S.Pat. No. 5,645,948, U.S. Pat. No. 5,683,823, U.S. Pat. No. 5,755,999,U.S. Pat. No. 5,928,802, U.S. Pat. No. 5,935,720, U.S. Pat. No.5,935,721, and U.S. Pat. No. 6,020,078.

Metal complexes of 8-hydroxyquinoline and similar derivatives, alsoknown as metal-chelated oxinoid compounds (Formula E), constitute oneclass of useful host compounds capable of supportingelectroluminescence, and are particularly suitable for light emission ofwavelengths longer than 500 nm, e.g., green, yellow, orange, and red.

wherein

-   -   M represents a metal;    -   n is an integer of from 1 to 4; and    -   Z independently in each occurrence represents the atoms        completing a nucleus having at least two fused aromatic rings.

From the foregoing it is apparent that the metal can be monovalent,divalent, trivalent, or tetravalent metal. The metal can, for example,be an alkali metal, such as lithium, sodium, or potassium; an alkalineearth metal, such as magnesium or calcium; a trivalent metal, suchaluminum or gallium, or another metal such as zinc or zirconium.Generally any monovalent, divalent, trivalent, or tetravalent metalknown to be a useful chelating metal can be employed.

Z completes a heterocyclic nucleus containing at least two fusedaromatic rings, at least one of which is an azole or azine ring.Additional rings, including both aliphatic and aromatic rings, can befused with the two required rings, if required. To avoid addingmolecular bulk without improving on function the number of ring atoms isusually maintained at 18 or less.

Illustrative of useful chelated oxinoid compounds are the following:

-   -   CO-1: Aluminum trisoxine [alias,        tris(8-quinolinolato)aluminum(III)]    -   CO-2: Magnesium bisoxine [alias,        bis(8-quinolinolato)magnesium(II)]    -   CO-3: Bis[benzo{f}-8-quinolinolato]zinc (II)    -   CO-4:        Bis(2-methyl-8-quinolinolato)aluminum(III)-μ-oxo-bis(2-methyl-8-quinolinolato)        aluminum(III)    -   CO-5: Indium trisoxine [alias, tris(8-quinolinolato)indium]    -   CO-6: Aluminum tris(5-methyloxine) [alias,        tris(5-methyl-8-quinolinolato) aluminum(III)]    -   CO-7: Lithium oxine [alias, (8-quinolinolato)lithium(I)]    -   CO-8: Gallium oxine [alias, tris(8-quinolinolato)gallium(III)]    -   CO-9: Zirconium oxine [alias,        tetra(8-quinolinolato)zirconium(IV)]

As already mentioned, derivatives of 9,10-di-(2-naphthyl)anthracene(Formula F) constitute one class of useful host materials capable ofsupporting electroluminescence, and are particularly suitable for lightemission of wavelengths longer than 400 nm, e.g., blue, green, yellow,orange or red.

wherein: R¹, R², R³, R⁴, R⁵, and R⁶ represent one or more substituentson each ring where each substituent is individually selected from thefollowing groups:

-   -   Group 1: hydrogen, or alkyl of from 1 to 24 carbon atoms;    -   Group 2: aryl or substituted aryl of from 5 to 20 carbon atoms;    -   Group 3: carbon atoms from 4 to 24 necessary to complete a fused        aromatic ring of anthracenyl; pyrenyl, or perylenyl;    -   Group 4: heteroaryl or substituted heteroaryl of from 5 to 24        carbon atoms as necessary to complete a fused heteroaromatic        ring of furyl, thienyl, pyridyl, quinolinyl or other        heterocyclic systems;    -   Group 5: alkoxylamino, alkylamino, or arylamino of from 1 to 24        carbon atoms; and    -   Group 6: fluorine, chlorine, bromine or cyano.

Illustrative examples include 9,10-di-(2-naphthyl)anthracene and2-t-butyl-9,10-di-(2-naphthyl)anthracene. Other anthracene derivativescan be useful as a host in the LEL, including derivatives of9,10-bis[4-(2,2-diphenylethenyl)phenyl]anthracene.

Benzazole derivatives (Formula G) constitute another class of usefulhost materials capable of supporting electroluminescence, and areparticularly suitable for light emission of wavelengths longer than 400nm, e.g., blue, green, yellow, orange or red.

wherein:

-   -   n is an integer of 3 to 8;    -   Z is O, NR or S; and    -   R and R′ are individually hydrogen; alkyl of from 1 to 24 carbon        atoms, for example, propyl, t-butyl, heptyl, and the like; aryl        or hetero-atom substituted aryl of from 5 to 20 carbon atoms for        example phenyl and naphthyl, furyl, thienyl, pyridyl, quinolinyl        and other heterocyclic systems; or halo such as chloro, fluoro;        or atoms necessary to complete a fused aromatic ring; and    -   L is a linkage unit consisting of alkyl, aryl, substituted        alkyl, or substituted aryl, which connects the multiple        benzazoles together. L may be either conjugated with the        multiple benzazoles or not in conjugation with them. An example        of a useful benzazole is        2,2′,2″-(1,3,5-phenylene)tris[1-phenyl-1H-benzimidazole].    -   Styrylarylene derivatives as described in U.S. Pat. No.        5,121,029 and JP 08333569 are also useful hosts for blue        emission. For example,        9,10-bis[4-(2,2-diphenylethenyl)phenyl]anthracene and        4,4′-bis(2,2-diphenylethenyl)-1,1′-biphenyl (DPVBi) are useful        hosts for blue emission.

Useful fluorescent emitting materials include, but are not limited to,derivatives of anthracene, tetracene, xanthene, perylene, rubrene,coumarin, rhodamine, and quinacridone, dicyanomethylenepyran compounds,thiopyran compounds, polymethine compounds, pyrylium and thiapyryliumcompounds, fluorene derivatives, periflanthene derivatives,indenoperylene derivatives, bis(azinyl)amine boron compounds,bis(azinyl)methane compounds, and carbostyryl compounds. Illustrativeexamples of useful materials include, but are not limited to, thefollowing:

X R1 R2 L9 O H H L10 O H Methyl L11 O Methyl H L12 O Methyl Methyl L13 OH t-butyl L14 O t-butyl H L15 O t-butyl t-butyl L16 S H H L17 S H MethylL18 S Methyl H L19 S Methyl Methyl L20 S H t-butyl L21 S t-butyl H L22 St-butyl t-butyl

X R1 R2 L23 O H H L24 O H Methyl L25 O Methyl H L26 O Methyl Methyl L27O H t-butyl L28 O t-butyl H L29 O t-butyl t-butyl L30 S H H L31 S HMethyl L32 S Methyl H L33 S Methyl Methyl L34 S H t-butyl L35 S t-butylH L36 S t-butyl t-butyl

R L37 phenyl L38 methyl L39 t-butyl L40 mesityl

R L41 phenyl L42 methyl L43 t-butyl L44 mesityl

In addition to the light-emitting materials of this invention,light-emitting phosphorescent materials may be used in the EL device.For convenience, the phosphorescent complex guest material may bereferred to herein as a phosphorescent material. The phosphorescentmaterial typically includes one or more ligands, for example monoanionicligands that can be coordinated to a metal through an sp² carbon and aheteroatom. Conveniently, the ligand can be phenylpyridine (ppy) orderivatives or analogs thereof. Examples of some useful phosphorescentorganometallic materials includetris(2-phenylpyridinato-N,C^(2′))iridium(III),bis(2-phenylpyridinato-N,C²)iridium(III)(acetylacetonate), andbis(2-phenylpyridinato-N,C^(2′))platinum(II). Usefully, manyphosphorescent organometallic materials emit in the green region of thespectrum, that is, with a maximum emission in the range of 510 to 570nm.

Phosphorescent materials may be used singly or in combinations otherphosphorescent materials, either in the same or different layers.Phosphorescent materials and suitable hosts are described in WO00/57676, WO 00/70655, WO 01/41512 A1, WO 02/15645 A1, US 2003/0017361A1, WO 01/93642 A1, WO 01/39234 A2, U.S. Pat. No. 6,458,475 B1, WO02/071813 A1, U.S. Pat. No. 6,573,651 B2, US 2002/0197511 A1, WO02/074015 A2, U.S. Pat. No. 6,451,455 B1, US 2003/0072964 A1, US2003/0068528 A1, U.S. Pat. No. 6,413,656 B1, U.S. Pat. No. 6,515,298 B2,U.S. Pat. No. 6,451,415 B1, U.S. Pat. No. 6,097,147, US 2003/0124381 A1,US 2003/0059646 A1, US 2003/0054198 A1, EP 1 239 526 A2, EP 1 238 981A2, EP 1 244 155 A2, US 2002/0100906 A1, US 2003 /0068526 A1, US2003/0068535 A1, JP 2003073387A, JP 2003 073388A, US 2003/0141809 A1, US2003/0040627 A1, JP 2003059667A, JP 2003073665A, and US 2002/0121638 A1.

The emission wavelengths of cyclometallated Ir(III) complexes of thetype IrL₃ and IrL₂L′, such as the green-emittingfac-tris(2-phenylpyridinato-N,C^(2′))iridium(III) andbis(2-phenylpyridinato-N,C^(2′))iridium(III)(acetylacetonate) may beshifted by substitution of electron donating or withdrawing groups atappropriate positions on the cyclometallating ligand L, or by choice ofdifferent heterocycles for the cyclometallating ligand L. The emissionwavelengths may also be shifted by choice of the ancillary ligand L′.Examples of red emitters are thebis(2-(2′-benzothienyl)pyridinato-N,C^(3′))iridium(III)(acetylacetonate)and tris(2-phenylisoquinolinato-N,C)iridium(III). A blue-emittingexample isbis(2-(4,6-difluorophenyl)-pyridinato-N,C^(2′))iridium(III)(picolinate).

Red electrophosphorescence has been reported, usingbis(2-(2′-benzo[4,5-a]thienyl)pyridinato-N, C³) iridium(acetylacetonate) [Btp₂Ir(acac)] as the phosphorescent material (C.Adachi, S. Lamansky, M. A. Baldo, R. C. Kwong, M. E. Thompson, and S. R.Forrest, App. Phys. Lett., 78, 1622–1624 (2001)).

Other important phosphorescent materials include cyclometallated Pt(II)complexes such as cis-bis(2-phenylpyridinato-N,C^(2′))platinum(II),cis-bis(2-(2′-thienyl)pyridinato-N,C^(3′)) platinum(II),cis-bis(2-(2′-thienyl)quinolinato-N,C^(5′)) platinum(II), or(2-(4,6-difluorophenyl)pyridinato-N,C²′) platinum (II)(acetylacetonate). Pt (II) porphyrin complexes such as2,3,7,8,12,13,17,18-octaethyl-21H, 23H-porphine platinum(II) are alsouseful phosphorescent materials.

Still other examples of useful phosphorescent materials includecoordination complexes of the trivalent lanthanides such as Tb³⁺ andEu³⁺ (J. Kido et al., Appl. Phys. Lett., 65, 2124 (1994)).

Suitable host materials for phosphorescent materials should be selectedso that transfer of a triplet exciton can occur efficiently from thehost material to the phosphorescent material but cannot occurefficiently from the phosphorescent material to the host material.Therefore, it is highly desirable that the triplet energy of thephosphorescent material be lower than the triplet energy of the host.Generally speaking, a large triplet energy implies a large opticalbandgap. However, the band gap of the host should not be chosen so largeas to cause an unacceptable barrier to injection of charge carriers intothe light-emitting layer and an unacceptable increase in the drivevoltage of the OLED. Suitable host materials are described in WO00/70655 A2; 01/39234 A2; 01/93642 A1; 02/074015 A2; 02/15645 A1, and US20020117662. Suitable hosts include certain aryl amines, triazoles,indoles and carbazole compounds. Examples of desirable hosts are4,4′-N,N′-dicarbazole-biphenyl, otherwise known as4,4′-bis(carbazol-9-yl)biphenyl or CBP;4,4′-N,N′-dicarbazole-2,2′-dimethyl-biphenyl, otherwise known as2,2′-dimethyl-4,4′-bis(carbazol-9-yl)biphenyl or CDBP;1,3-bis(N,N′-dicarbazole)benzene, otherwise known as1,3-bis(carbazol-9-yl)benzene, and poly(N-vinylcarbazole), includingtheir derivatives.

-   -   Desirable host materials are capable of forming a continuous        film.        Hole-Blocking Layer (HBL)

In addition to suitable hosts, an OLED device employing a phosphorescentmaterial often requires at least one hole-blocking layer placed betweenthe electron-transporting layer 111 and the light-emitting layer 109 tohelp confine the excitons and recombination events to the light-emittinglayer comprising the host and phosphorescent material. In this case,there should be an energy barrier for hole migration from the host intothe hole-blocking layer, while electrons should pass readily from thehole-blocking layer into the light-emitting layer comprising a host anda phosphorescent material. The first requirement entails that theionization potential of the hole-blocking layer be larger than that ofthe light-emitting layer 109, desirably by 0.2 eV or more. The secondrequirement entails that the electron affinity of the hole-blockinglayer not greatly exceed that of the light-emitting layer 109, anddesirably be either less than that of light-emitting layer or not exceedthat of the light-emitting layer by more than about 0.2 eV.

When used with an electron-transporting layer whose characteristicluminescence is green, such as an Alq-containing electron-transportinglayer as described below, the requirements concerning the energies ofthe highest occupied molecular orbital (HOMO) and lowest unoccupiedmolecular orbital (LUMO) of the material of the hole-blocking layerfrequently result in a characteristic luminescence of the hole-blockinglayer at shorter Wavelengths than that of the electron-transportinglayer, such as blue, violet, or ultraviolet luminescence. Thus, it isdesirable that the characteristic luminescence of the material of ahole-blocking layer be blue, violet, or ultraviolet. It is furtherdesirable, but not absolutely required, that the triplet energy of thehole-blocking material be greater than that of the phosphorescentmaterial. Suitable hole-blocking materials are described in WO00/70655A2 and WO 01/93642 A1. Two examples of useful hole-blockingmaterials are bathocuproine (BCP) andbis(2-methyl-8-quinolinolato)(4-phenylphenolato)aluminum(III) (BAlq).The characteristic luminescence of BCP is in the ultraviolet, and thatof BAlq is blue. Metal complexes other than BAlq are also known to blockholes and excitons as described in US 20030068528. In addition, US20030175553 A1 describes the use offac-tris(1-phenylpyrazolato-N,C^(2′))iridium(III) (Irppz) for thispurpose.

When a hole-blocking layer is used, its thickness can be between 2 and100 nm and suitably between 5 and 10 nm.

Electron-Transporting Layer (ETL)

Desirable thin film-forming materials for use in forming theelectron-transporting layer 111 of the organic EL devices of thisinvention are metal-chelated oxinoid compounds, including chelates ofoxine itself (also commonly referred to as 8-quinolinol or8-hydroxyquinoline). Such compounds help to inject and transportelectrons, exhibit high levels of performance, and are readilyfabricated in the form of thin films. Exemplary of contemplated oxinoidcompounds are those satisfying structural formula (E), previouslydescribed.

Other electron-transporting materials suitable for use in theelectron-transporting layer 111 include various butadiene derivatives asdisclosed in U.S. Pat. No. 4,356,429 and various heterocyclic opticalbrighteners as described in U.S. Pat. No. 4,539,507. Benzazolessatisfying structural formula (G) are also useful electron transportingmaterials. Triazines are also known to be useful as electrontransporting materials.

If both a hole-blocking layer and an electron-transporting layer 111 areused, electrons should pass readily from the electron-transporting layer111 into the hole-blocking layer. Therefore, the electron affinity ofthe electron-transporting layer 111 should not greatly exceed that ofthe hole-blocking layer. Desirably, the electron affinity of theelectron-transporting layer should be less than that of thehole-blocking layer or not exceed it by more than about 0.2 eV.

If an electron-transporting layer is used, its thickness may be between2 and 100 nm and suitably between 5 and 20 nm.

Other Useful Organic Layers and Device Architecture

In some instances, layers 109 through 111 can optionally be collapsedinto a single layer that serves the function of supporting both lightemission and electron transportation. The hole-blocking layer, whenpresent, and layer 111 may also be collapsed into a single layer thatfunctions to block holes or excitons, and supports electron transport.It also known in the art that emitting materials may be included in thehole-transporting layer 107. In that case, the hole-transportingmaterial may serve as a host. Multiple materials may be added to one ormore layers in order to create a white-emitting OLED, for example, bycombining blue- and yellow-emitting materials, cyan- and red-emittingmaterials, or red-, green-, and blue-emitting materials. White-emittingdevices are described, for example, in EP 1 187 235, US 20020025419, EP1 182 244, U.S. Pat. No. 5,683,823, U.S. Pat. No. 5,503,910, U.S. Pat.No. 5,405,709, and U.S. Pat. No. 5,283,182 and can be equipped with asuitable filter arrangement to produce a color emission.

This invention may be used in so-called stacked device architecture, forexample, as taught in U.S. Pat. No. 5,703,436 and U.S. Pat. No.6,337,492.

Deposition of Organic Layers

The organic materials mentioned above are suitably deposited by anymeans suitable for the form of the organic materials. In the case ofsmall molecules, they are conveniently deposited through sublimation orevaporation, but can be deposited by other means such as coating from asolvent together with an optional binder to improve film formation. Ifthe material is a polymer, solvent deposition is usually preferred. Thematerial to be deposited by sublimation or evaporation can be vaporizedfrom a sublimator “boat” often comprised of a tantalum material, e.g.,as described in U.S. Pat. No. 6,237,529, or can be first coated onto adonor sheet and then sublimed in closer proximity to the substrate.Layers with a mixture of materials can utilize separate sublimator boatsor the materials can be pre-mixed and coated from a single boat or donorsheet. Patterned deposition can be achieved using shadow masks, integralshadow masks (U.S. Pat. No. 5,294,870), spatially-defined thermal dyetransfer from a donor sheet (U.S. Pat. No. 5,688,551, U.S. Pat. No.5,851,709 and U.S. Pat. No. 6,066,357) or an inkjet method (U.S. Pat.No. 6,066,357).

Encapsulation

Most OLED devices are sensitive to moisture or oxygen, or both, so theyare commonly sealed in an inert atmosphere such as nitrogen or argon,along with a desiccant such as alumina, bauxite, calcium sulfate, clays,silica gel, zeolites, alkaline metal oxides, alkaline earth metaloxides, sulfates, or metal halides and perchlorates. Methods forencapsulation and desiccation include, but are not limited to, thosedescribed in U.S. Pat. No. 6,226,890. In addition, barrier layers suchas SiO_(x), Teflon, and alternating inorganic/polymeric layers are knownin the art for encapsulation. Any of these methods of sealing orencapsulation and desiccation can be used with the EL devicesconstructed according to the present invention.

Optical Optimization

OLED devices of this invention can employ various well-known opticaleffects in order to enhance their emissive properties if desired. Thisincludes optimizing layer thicknesses to yield maximum lighttransmission, providing dielectric mirror structures, replacingreflective electrodes with light-absorbing electrodes, providinganti-glare or anti-reflection coatings over the display, providing apolarizing medium over the display, or providing colored, neutraldensity, or color-conversion filters over the display. Filters,polarizers, and anti-glare or anti-reflection coatings may bespecifically provided over the EL device or as part of the EL device.

Embodiments of the invention may provide advantageous features such ashigher luminous yield, lower drive voltage, higher power efficiency,improved stability, reduced sublimation temperatures, and simplifiedmanufacturing, as well as desirable hues including those useful in theemission of white light (directly or through filters to providemulticolor displays). Embodiments of the invention can also providedevices incorporating the OLED device such as electronic displays andarea lighting devices.

The invention and its advantages can be better appreciated by thefollowing examples.

SYNTHETIC EXAMPLE

Preparation of Inv-1

1-Bromo-3-fluorobenzene (6.3 g, 36.5 mmol) was dissolved in 40 mL THFand cooled to −78° C. under a positive pressure of nitrogen. n-BuLi (1.6M in hexanes; 35.1 mmol) was added dropwise, and the solution wasstirred for 30 min before being transferred via cannula to a solution of6,11-diphenyl-5,12-naphthacenequinone (3 g, 7.3 mmol) in THF at −78° C.The reaction was warmed to 25° C., and quenched with methanol. Theproduct was partitioned between methylene chloride and water. Theorganic layers were dried over MgSO₄, filtered, and then concentrated toan oil. The oil was triturated with ether and hexane to produce 3.7 g ofdiol at 97% purity by HPLC analysis. The diol was suspended in 150 mLether. A solution of hydrogen iodide in water (10.5 mmol) was added, andthe reaction was refluxed for 5 min. After cooling, excess sodiummetabisulfite was added and the product was extracted into methylenechloride. The organic layers were dried and concentrated to produce ared solid. After chromatography, the 1.7 g of the tetracene, Inv 1–1,was isolated. The structure was consistent with NMR and massspectrometry data and was confirmed by X-ray analysis.

SUBLIMATION TEMPERATURES EXAMPLE

The sublimation temperatures at 5×10⁻⁶ Torr needed to deposit theinventive and comparative dopants at 1% and 2%-wt. of the host arerecorded in Table 1. This sublimation temperature is the temperaturerequired to sublime a specific amount of material, recorded asthickness, onto the device at a specific rate and is given inAngstroms/sec., (A/s). For dopants at 1%-wt of host, this rate is 0.04A/s and at 2%-wt it is 0.08 A/s.

The comparative compounds used in the invention are listed below. Com-1is the parent rubrene compound. Com-2 is the para-fluoro substitutedisomer of Inv-1. Com-3 and Com-4 are other yellow dopants known in theliterature.

TABLE 1 SUBLIMATION TEMPERATURES Sublimation Temp (° C.) Dopant LevelSample Type Dopant 1% 2% 1-1 Inventive Inv-1 186 197 1-2 ComparativeCom-1 211 218 1-3 Comparative Com-2 201 203 1-4 Comparative Com-3 — 3271-5 Inventive Inv-10 238 249 1-6 Comparative Com-4 255 262 1-7 InventiveInv-18 245 255

It can be seen from Table 1 that the materials of the invention havelower sublimation temperatures relative to comparison materials havingsimilar structures. For example Inv-1 sublimes at a lower temperaturethan Com-1 or Com-2. Inv-10 sublimes at a lower temperature than Com-3or Com-4, and Inv-18 sublimes at a temperature significantly lower thanthat of the close analog, Com-3.

It can be seen from Table 1 that the tested materials of the inventionhave lower sublimation temperatures relative to comparison materialshaving similar structures. For example Inv-1 sublimes at a lowertemperature than Com-1 or Com-2. Inv-10 sublimes at a lower temperaturethan Com-3 or Com4, and Inv-18 sublimes at a temperature significantlylower than the close analog, Com-3.

DEVICE EXAMPLE 1

EL Device Fabrication of Samples 1–4

An EL device (Sample 1) satisfying the requirements of the invention wasconstructed in the following manner:

-   -   1. A glass substrate coated with an 85 nm layer of indium-tin        oxide (ITO) as the anode was sequentially ultrasonicated in a        commercial detergent, rinsed in deionized water, degreased in        toluene vapor and exposed to oxygen plasma for about 1 min.    -   2. Over the ITO was deposited a 1 nm fluorocarbon (CFx)        hole-injecting layer (HIL) by plasma-assisted deposition of        CHF₃.    -   3. A hole-transporting layer (HTL)of        N,N′-di-1-naphthyl-N,N′-diphenyl-4,4′-diaminobiphenyl (NPB)        having a thickness of 150 as then evaporated from a tantalum        boat.    -   4. A 37.5 nm light-emitting layer (LEL) of        tris(8-quinolinolato)aluminum (III) (AlQ₃) and Inv-1 (1.0%) were        then deposited onto the hole-transporting layer. These materials        were also evaporated from tantalum boats.    -   5. A 37.5 nm electron-transporting layer (ETL) of        tris(8-quinolinolato)aluminum (III) (AlQ₃) was then deposited        onto the light-emitting layer. This material was also evaporated        from a tantalum boat.    -   6. On top of the AlQ₃ layer was deposited a 220 nm cathode        formed of a 10:1 volume ratio of Mg and Ag.

The above sequence completed the deposition of the EL device. The devicewas then hermetically packaged in a dry glove box for protection againstambient environment.

EL devices, Samples 2–4, incorporating Inv-1 were fabricated in anidentical manner as Sample 1, except Inv-1 was used at the levelsindicated in the Table 2. The cells thus formed were tested forluminance and color at an operating current of 20 mA/cm² and the resultsare reported in Table 2 in the form of luminance yield (cd/A), λmax ofemission, and CIE (Commission Internationale de L'Eclairage) coordinatesof the emission.

TABLE 2 EVALUATION RESULTS FOR EL DEVICES 1–4. Level Yield λmax SampleMaterial (%) (cd/A) (nm) CIEx CIEy Type 1 Inv-1 1.00 7.04 560 0.4790.507 Invention 2 Inv-1 2.00 6.44 564 0.502 0.490 Invention 3 Inv-1 3.005.82 568 0.509 0.484 Invention 4 Inv-1 5.00 4.91 568 0.517 0.476Invention

As can be seen from Table 2, tested devices incorporating the inventionlight-emitting material, Inv-1, demonstrate good efficiency and color.

DEVICE EXAMPLE 2

EL Device Fabrication of Samples 5–12

EL devices, Samples 5–12, were fabricated in an identical as Samples1–4, except Inv-10 was used in place of Inv-1. The cells thus formedwere tested for luminance and color at an operating current of 20 mA/cm²and the results are reported in Table 3 in the form of luminance yield(cd/A), λmax of emission, and CIE coordinates of the emission.

TABLE 3 EVALUATION RESULTS FOR EL DEVICES 5–8. Level Yield λmax SampleMaterial (%) (cd/A) (nm) CIEx CIEy Type 5 Inv-10 1.00 8.87 564 0.4840.505 Invention 6 Inv-10 2.00 8.60 560 0.463 0.520 Invention 7 Inv-103.00 8.14 568 0.494 0.497 Invention 8 Inv-10 5.00 6.88 572 0.508 0.484Invention 9 Com-4 1.00 8.32 568 0.507 0.484 Comparative 10 Com-4 2.008.19 572 0.522 0.473 Comparative 11 Com-4 3.00 7.18 576 0.532 0.463Comparative 12 Com-4 5.00 6.29 576 0.541 0.454 Comparative

As can be seen from Table 3, tested devices incorporating the inventionlight-emitting material, Inv-10, demonstrate good efficiency and color,and that the efficiency of Inv-10 is superior to that of Com-4.

The entire contents of the patents and other publications referred to inthis specification are incorporated herein by reference. The inventionhas been described in detail with particular reference to certainpreferred embodiments thereof, but it will be understood that variationsand modifications can be effected within the spirit and scope of theinvention.

PARTS LIST

-   101 Substrate-   103 Anode-   105 Hole-Injecting layer (HIL)-   107 Hole-Transporting layer (HTL)-   109 Light-Emitting layer (LEL)-   111 Electron-Transporting layer (ETL)-   113 Cathode

1. An electroluminescent device comprising a host material and a rubrenederivative having a naphthacene nucleus comprising four fused phenylrings a, b, c, and d, in order, wherein the rubrene derivative isrepresented by Formula (1),

wherein: Ar₁, Ar₂, and Ar₃ represent independently selected aryl groups;each G represents an independently selected substituent; each m isindependently 0–4; V¹–V⁵ represent hydrogen or independently selectedsubstituent groups, provided there are in total two fluoro orperfluoroalkyl groups linked directly or indirectly to the “c” ring,selected from those where: a) at least one of V¹–V⁴ represents a fluoroor perfluoroalkyl group, or b) at least one of V¹–V⁵ and Ar₃ includes anaryl ring bearing a fluoro or trifluoroalkyl group.
 2. The device ofclaim 1 wherein the perfluoroalkyl group is a trifluoromethyl group. 3.The device of claim 1 wherein the secondary phenyl ring on the “c” ringbears a fluoro or perfluoromethyl group on a meta- or ortho-position ofthat ring.
 4. The device of claim 1 wherein the each secondary phenylring on the “c” ring bears a fluoro or trifluoromethyl group on a meta-or ortho-position.
 5. The device of claim 1 wherein at least onesecondary phenyl ring on the “c” ring bears a meta- or ortho-fluorosubstituent.
 6. The device of claim 1 at least one secondary phenyl ringon the “c” ring is linked to an aryl group that is substituted with afluoro or perfluoroalkyl group.
 7. The device of claim 6 wherein thearyl group is a phenyl group that bears a meta- or para-fluorosubstituent.
 8. The device of claim 1, wherein the rubrene derivative isrepresented by Formula (1),

wherein: Ar₁, Ar₂, and Ar₃ represent independently selected aryl groups;each G represents an independently selected substituent; each m isindependently 0–4; V¹–V⁵ represent hydrogen or independently selectedsubstituent groups, provided there are in total two fluoro orperfluoroalkyl groups linked directly or indirectly to the “c” ring,selected from those where: a) at least one of V¹–V⁴ represents a fluoroor perfluoroalkyl group, or at least one of V¹–V⁵ and Ar₃ includes anaryl ring bearing a fluoro or trifluoromethyl group.
 9. The device ofclaim 1, wherein V³ represents a fluoro substituent.
 10. The device ofclaim 9, wherein at least one of V², V³ or V⁵ includes a phenyl ringbearing a fluoro or perfluoroalkyl group.
 11. The device of claim 9wherein the substituents are selected to provide an emitted light havingan orange-red hue.
 12. The device of claim 9 wherein the substituentsare selected to provide an emitted light having a wavelength of maximumemission (λ_(max)) in ethyl acetate solution such that520 nm≦λ_(max)≦650 nm.
 13. The device of claim 9 wherein thesubstituents are selected to provide a reduced loss of initial luminancecompared to the device containing no rubrene derivative.
 14. The deviceof claim 1 wherein: either a) the sublimation temperature of saidderivative is lower by at least 5° C. than the derivative without thefluoro or perfluoroalkyl groups; or b) the derivative sublimes and thederivative without the fluoro or perfluoroalkyl groups melts.
 15. Adevice of claim 1 wherein the derivative has a sublimation temperatureof at least 10° C. lower than that of the rubrene without fluorine orfluorine containing groups.
 16. The device of claim 1, furthercomprising a blue or blue-green light-emitting compound to provide awhite light emission.
 17. The device of claim 16 wherein the blue orblue-green light-emitting material comprises a perylene group.
 18. Thedevice of claim 16 wherein the blue or blue-green light-emittingmaterial comprises a material of one of the following structures:

wherein: R^(a)–R^(h) independently represent hydrogen or one or more anindependently selected substituents.
 19. The device of claim 18 whereinthe blue or blue-green light-emitting material comprises1,4-bis[2-[4-[N,N-di(p-tolyl)amino]phenyl]vinyl]benzene (BDTAPVB) or1,4-bis[2-[4-[N,N-di(p-tolyl)amino]phenyl]vinyl]biphenyl.
 20. The deviceof claim 16, wherein, the blue or blue-green light-emitting compoundcomprises a boron complex.
 21. The device of claim 20 wherein the blueor blue-green light-emitting material comprises a compound representedthe following structure:

wherein: Ar^(a) and Ar^(b) independently represent the atoms necessaryto form an aromatic ring group; w represents N or C—Y, wherein Yrepresents hydrogen or a substituent; and Z^(a) and Z^(b) representindependently selected substituents.
 22. The device of claim 21 whereinw represents N.
 23. The device of claim 1, further comprising a redlight-emitting compound to provide a white light emission.
 24. Thedevice of claim 23 wherein the red light-emitting compound comprises adiindenoperylene compound of the following structure:

wherein: R₁–R₁₆ are independently selected as hydrogen or a substituent.25. The device of claim 24, wherein R₁, R₄, R₉, R₁₂ representindependently selected phenyl groups, R₂, and R₃ as well as R₁₀ and R₁₁form independently selected fused benzene ring groups.
 26. The device ofclaim 1, wherein the host material is a hole-transporting material. 27.The device of claim 1, wherein the host material is a hole-transportingmaterial comprising a tertiary amine.
 28. The device of claim 1, whereinthe host material is an electron-transporting material.
 29. The deviceof claim 28, wherein the electron-transporting material comprises ametal complex of 8-hydroxyquinoline.
 30. The device of claim 1 whereinthe derivative is present in an amount of up to 10%-wt of the hostmaterial.
 31. The device of claim 1 wherein the derivative is present inan amount of up to 0.1–5.0%-wt of the host material.
 32. A displaycomprising the electroluminescent device of claim
 1. 33. The device ofclaim 1 wherein white light is produced either directly or by usingfilters.
 34. An area lighting device comprising the electroluminescentdevice of claim
 1. 35. A process for emitting light comprising applyinga potential across the device of claim 1.